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DENTAL SOCIETY 




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THE NORMAL AND PATHOLOGICAL 
HISTOLOGY OF THE MOUTH 



VOLUME I 
NORMAL HISTOLOGY 



.ArlY 

ENTAL SCtfCOL 
W.V.U. 



By the same Author 

An Introduction to Dental Anatomy 

and Physiology: Descriptive 

and Applied," 1913. 

'Dental Microscopy," a Handbook of 
Practical Dental Histology. 

First Edition, January, 1895. 
Second Edition, July, 1899. 
Third Edition, May, 1914. 



Part Editor of Tomes' 
"A Manual of Dental Anatomy" 

Seventh Edition, 1914. 



Digitized by the Internet Archive 

in 2012 with funding from 

LYRASIS Members and Sloan Foundation 



http://archive.org/details/normpath01hope 



DESCRIPTION OF PLATE I 

Sagittal section through the mandible of a kitten at birth. The vascular system 
is injected with Prussian blue solution. Tissues hardened in alcohol. Section 
stained with carmine. Magnified 20 times, a. Internal set of bloodvessels 
supplying the dental pulp; b. External set to the enamel organ; c. Vessels of the 
gum; d. Of the alveolar wall and dental capsule; e. Internal anastomoses of 
external set of vessels; F. Point of junction of external and internal systems. 
For details see pp. 134 and 262 et scq. 



SL Lsuls Dental Society 

The Normal and Pathological 
Histology of the Mouth 

BEING THE SECOND EDITION OF 

The Histology and Patho-Histology 

OF THE 

Teeth and Associated Parts 

REVISED AND ENLARGED 



ARTHUR HOPEWELL-SMITH 

L. R. C. P., Lond., M. R. C. S., Eng., L. b*.*S., Eng. 



PROFESSOR OF DENTAL HISTOLOGY, PATHOLOGY AND COMPARATIVE ODONTOLOGY 
UNIVERSITY OF PENNSYLVANIA, PHILADELPHIA; JOHN TOMES PRIZEMAN OF 
THE ROYAL COLLEGE OF SURGEONS OF ENGLAND; MEMBRE HONORAIRE 
DE LA SOCIETE ODONTOLOGIQUE DE FRANCE; FORMERLY LECTURER 
ON DENTAL ANATOMY, SURGEON AND DEMONSTRATOR OF DENTAL 
HISTOLOGY AT THE ROYAL DENTAL HOSPITAL OF LONDON; 
MEMBER OF THE FACULTY OF MEDICINE OF THE UNIVER- 
SITY OF LONDON; EXTERNAL EXAMINER IN DENTAL 
SURGERY AT THE UNIVERSITIES OF BIRMINGHAM, 
LEEDS AND LIVERPOOL; LECTURER ON ] 
SURGERY AND PATHOLOGY AT THE N 
TIONAL DENTAL HOSPITAL, LONDON 



VOLUME I 



NORMAL HISTOLOGY 



WITH 2 COLOURED PLAlES AND 262 ILLUSTRATIONS 

IN THE TEXT, INCLUDING 149 

ORIGINAL PHOTOMICROGRAPHS BY THE AUTHOR 

1045312 

PHILADELPHIA 

P. BLAKISTON'S SON & CO. 

1012 WALNUT STREET 






Copyright, 1918, by P. Blakiston's Son & Co. 



'R E S S XI 



CO 

Sir James Crichton Browne, M.D., LL.D., F.R.S. 
J. Howard Mummery, Sc.D., Penn., M.R.C.S., Eng.,L.D.S.,Eng. 

AND 

Frederick J. Bennett, M.R.C.S., Eng„ L.D.S., Eng. 

AS AN 

Expression 
of the Esteem and Sincere Regard 



Ol)e ,Autbor 



PREFACE TO THE SECOND EDITION 

Owing to a completer extension of the subjects included in 
this work, it has been considered necessary to change its title. 
The present one more correctly represents its scope. 

For the convenience of the reader the book is now issued 
in two volumes. The first relates to the Normal Histology 
of the Mouth and its Contents, and the second to the Patho- 
logical Conditions found therein, with special reference to the 
Teeth of Man. Part III in that Volume records the latest 
observations of the dental tissues at times encountered in 
ovarian teratomatous cysts. 

A thorough revision of the First Edition has been effected. 
Six additional chapters appear in Volume II, being specially 
revised accounts of original researches undertaken by the author 
in recent years. Chapter XVII, Vol. II, contains part of a 
paper presented by Mr. MacAdam Eccles, M. S., and the 
author to the Royal Society of Medicine of London. The 
substance of the chapter dealing with "Pyorrhea alveolaris" 
was originally submitted to the Xlth International Medical 
Congress at Buda-Pesth. The illustrations remain unique. 

Supplementing those first described in the First Edition, 
originality can be claimed for the observation, investigation, 
recording, and naming of several new pathological conditions 
of the human dental tissues, e.g., Nanoid dentine, Odontoceles — 
extra-capsular and sub-capsular — Diphyodontic gemination, 
Hydropic degeneration of the oral mucous membrane, Fibroid 
degeneration of the alveolo-dental periosteum, etc. 

Some changes in terminology have been deemed advisable 
and needful. Thus "epiblast" and ''mesoblast" are now 
"ectoderm" and mesoderm;" the "medullated" and "non- 
medullated" nerves become "myelinic" and "amyelinic" 
respectively. The "dental follicle" is more correctly desig- 
nated the "dental capsule;" for it bears no histological resem- 



X PREFACE TO THE SECOND EDITION 

blance to, nor does it at all approach the functions of such 
widely dissimilar structures as the hair follicles, the Graafian 
follicles, the agminated and solitary follicles, etc. 

A description of the pathological condition, entitled in the 
First Edition, a "granuloma" is omitted from the present 
volume. A so-called granuloma does not conform to the 
correct definition of a tumour, and is in no sense a new growth, 
being merely one form of granulation tissue, the result of 
chronic inflammation of the periodontal membrane. It is 
true that certain diseases such as tuberculosis, syphilis, glanders, 
leprosy, actinomycosis, etc., are grouped by some pathologists 
as the infective granulomata, because they give origin to 
formations resembling tumours composed of granulation tissue, 
or at least a tissue of closely allied appearance, and are of 
infective derivation. It is also true that some hyperplasic 
growths of the skin, including Mycosis fungoides and Dermatitis 
papillomatosa, as pointed out by Weichselbaum ("Elements 
of Pathological Histology," 1892), which develop as a direct 
consequence of inflammation are sometimes called granulomata. 
But there is nothing, either from a clinical or pathological 
point of view, to justify the application of the term to chronic 
inflammation of the alveolo-dental periosteum, or its retention 
in modern dental literature. 

One hundred and sixty new and original photographs and 
photomicrographs have been added to the text. 

The author's grateful thanks are extended to his friend and 
colleague Professor Nathaniel Gildersleeve, M. D., for rewriting 
Chapter XVI, Vol. II. His contribution represents le dernier 
mot with regard to the science of this branch of Oral and Dental 
Pathology: it is authoritative, perspicuous, comprehensive, 
important and valuable. 

To "The Dental Cosmos" for the use of many illustrations, 
and to the Publishers for their courtesy and excellent typo- 
graphical and pictorial presentation of the pages of the book 
the Author desires to tender his best thanks. 

The University of Pennsylvania, Philadelphia. 



PREFACE TO THE FIRST EDITION 

In presenting to the reader this humble effort to detail 
the essentials of his favourite study, the writer is fully sensible 
of the many shortcomings, textual as well as pictorial, which 
are necessarily attendant upon such an undertaking. It is 
extremely difficult to prevent subjective impressions and 
interpretations from obtruding themselves here and there, no 
matter how subsidiary to other weighty matters the author 
has endeavoured to make them. The personal equation is 
generally present and apparent in all work. The book rep- 
resents an earnest struggle for an intimate knowledge of the 
truth, clear and unprejudiced. And if the expressions of 
personal opinions seem to be rendered too conspicuous they 
must be regarded on their individual merits, and tested and 
accepted or rejected, as the case may be. The astute reader 
must be the judge. The fallibility of him who now enters upon 
his task must not be forgotten, and where errors have been 
committed they must be condoned. But the honesty of the 
writer's purpose or of his convictions must never for one moment 
be impugned. 

The establishment on a scientific and logical basis of the 
order, sequence, and internal composition of each chapter has 
been attempted. The manner of dealing with the variety of 
pathological facts and histological data in Chapters XIV., 
XV., and XVI. has been founded on two considerations. 
First, it has been deemed advisable to place on record an 
intelligent enunciation of what is implied by certain words. 
Some writers, especially those of the Continent of Europe, 
are apt to confuse ideas, the result being a constant use of 
some terms found in ordinary dental nomenclature which 
possess a lack of uniformity of definition, etc. Second, this 
method of arrangement affords a convenient, and, therefore, 
suitable "setting'' or background for the description of the 



Xll PREFACE TO THE FIRST EDITION 

histological characteristics of teeth and allied organs, which, 
after all, are intended to be the most distinguishing feature 
of the work. 

An acquaintance on the part of the student with the simple 
elements of histology and pathology is pre-supposed. 
An extensive bibliographical mass, to which references 
are made throughout, has been consulted. In order not to 
burden the text with too great a number of the writings of 
many histologists, an attempt has been made to place their 
hypotheses on an eclectic basis, namely, those which in the 
eyes of the author are worthy, some of notice merely, others 
of serious consideration. Many fundamental propositions are 
not universally accepted, and some of these are here noted; 
so that the reader, interested in any special branch of Dental 
Histology or Histo-Pathology, may receive hints and be 
guided and stimulated in taking up original research. 

In this way, some prominence is accorded to the recent 
writings of Oscar Romer, who, with others, denies the 
existence per se of the sheaths of Neumann. On the other 
hand, the work of many is already sufficiently completed, and 
knowledge is, as far as can be ascertained, accurate enough. 
Thus, with no fear of being prolix, the researches of 
Aitchison Robertson on the growth of dentine may be cited 
extensively. But examples need not be multiplied. 

The inclusion of Part III. — a preliminary histological ex- 
amination of many of the commoner and some of the rarer 
morbid affections of the teeth, gums, and osseous framework of 
the mouth — affords the reader an opportunity of comparing the 
morphological differences between healthy and diseased 
conditions of the masticatory organs. This section of the 
book should, therefore, be read and studied in conjunction 
with Part I., and deductions drawn therefrom. The juxta- 
position of the two should be of assistance to the thoughtful 
and enquiring student, and serve to extend and widen the 
area of his mental horizon. 

The author desires to express his indebtedness to the 
published works of Mr. Charles Tomes, and to Drs. G. V. Black, 
Miller, Leon Williams, and Norman Broomell, for the use of 



PREFACE TO THE FIRST EDITION Xlll 

some of the electrotypes which have accompanied their 
communications to The Dental Cosmos; and also for the same 
to the Council of the Odontological Society of Great 
Britain. In addition, he is grateful for the loan of valuable 
material and sections to many personal friends at home and 
abroad. Finally, he wishes to thank Mr. Frank J. Butler, 
for his original water-colour drawings; and the Publishers for 
their unvarying courtesy and assistance in the production 
of the book. 
Berkeley Square, London, W. 



(C&ntcitts 



fntt | 

THE DENTAL TISSUES 
CHAPTER I 

Page 

Prolegomena 3 

Introductory — Dental Histology a Part of Dental Anatomy — 
Founders of the Science and Art — Importance of the Subject — 
Historical — Problems of the Present and Revelations of the Future 

CHAPTER II 

Nasmyth's Membrane 9 

Definition — Views as to its Origin — Dimensions — The Cellular 
Layer — The Translucent Pellicle 

CHAPTER III 

The Enamel 17 

Definition — Origin — Distribution — Relationships — Gross Anatomy 
— Structure of the Rods and Matrix — Views as to their Nature and 
Origin — Their Mode of Arrangement — The Striae of Retzius — 
Views as to their Origin — The Lines of Schreger — Enamel 
"Spindles" — Views as to their Origin and Nature — The Amelo- 
dentinal Boundary 

CHAPTER IV 

Ortho-dentine 49 

Definition — Varieties — Origin — Gross Anatomy — Structure of the 
Matrix — The Tubes, their Measurements, Curvatures, Branches 
and Contents — Views as to the Nature of the Latter — The Sheaths 
of Neumann — Views as to their Nature — The Interglobular Spaces, 
Dimensions, and Contents — The Granular Layer of Tomes — The 
Lines of Schreger — The Contour Lines of Owen — Laminae— Views 
as to their Nature — Secondary Dentine 



CHAPTER V 

Page 

The Cementum 79 

Definition — Origin — Distribution — Gross Anatomy — Structure of 
the Matrix — Incremental Lines — Perforating Canals and Fibres 

CHAPTER VI 

Structural Modifications of the Enamel, Dentine, and Cementum .... 93 
The Enamel of the Teeth of Rodents— Of the Manatee— Of Fishes 
— Tubular Enamel — Views as to its Origin and Development — Plici- 
dentine — Vaso-dentine — Osteo-dentine — Classification of Dentines 
■ — Lacunated Cementum 

CHAPTER VII 

The Dental Pulp in 

Definition — Origin — Dimensions — Odontoblasts, their Shape, Size, 
'Relationships, Structure, Processes, and Analogies — Pulp Cell's 
Proper — The Stroma — The Basal Layer of Weil — The Vascular 
System — Histology of the Arteries, Veins and Capillaries — The 
Nerve Fibres, their Arrangement, Structure, and Terminations in 
Fishes, Reptiles, and Mammals — Views as to their Ultimate 
Endings 

CHAPTER VIII 

The Alveolo-dental Periosteum 166 

Definition — Origin — Dimensions — The Fibrous Elements — The 
Cellular Elements — The Blood Supply — The Nervous System 

futt JJ 

THE ORAL TISSUES 

CHAPTER IX 

The Oral Cavity and its Accessories 181 

The Minute Anatomy of the Lips and Cheeks — The Tongue — The 
Salivary Glands, their Ducts, and Mucous and Serous Acini — The 
•Hard and Soft Palate — The Palatine Tonsils 

CHAPTER X 

The Histology of the Maxillary and Mandibular Bones 195 

Origin — Distribution of Varieties of Bone — General Structure of 
Bone — Structure of Bone of the Canine Fossa — Of the Interdental 
Septa— Of the Hard Palate— Of the Wall of the Maxillary Sinus 
— Of the Mandible — Of the Alveolar Process 



CONTENTS XV11 

CHAPTER XI 

Page 

A Group of Minor Structures 209 

The Histology of the Absorbent Organ — Of the Dental Capsule — 
Of the Gum, its Mucous and Sub-mucous Tissues — Of the Mucous 
Membrane of the Maxillary Sinus, its Epithelium, Sub-mucous 
Tissues and Glands 



pnti jjj 



THE HISTOGENESIS OF THE TEETH OF MAMMALS, 
FISHES AND REPTILES 

CHAPTER XII 

The Development of the Teeth in Mammalia 231 

Earliest Phases of Evolution — Changes in the Ectoderm — Forma- 
tion of the Dental Furrow — The Primary Epithelial Inflection — ■ 
Origin of the Lip-furrow and Tooth-band — Views as to Derivation — 
Changes in the Mesoderm — Evolution of the Enamel Organ — The 
Metamorphoses Occurring in and around the Tooth Germ at the 
Period of Formation of the Dentine Germ — Structure of the Enamel 
Organ — Changes in the Dentine Papilla — Subsequent Embryo- 
logical Changes — Evolution of the Permanent Tooth Germs — The 
Blood Supply of the Developing Dental Tissues — The Origin of the 
Blood-vessels, their Arrangement, Mode of Distribution, and the 
Areas Governed by Them — Latest Research in the Vascular Supply 
— Final Stages of Dental Evolution — Origin of the Dental Capsule 
— Histories of the Various Structures Concerned in the Development 
of the Teeth — Development of the Enamel — Views as to its Nature 
— Development and Growth of the Dentine and Cementum — Table 
Showing Phases of Growth of the Several Parts of Tooth Germs in 
Human Foetuses at Half Term — Measurements of the Same — 
Histogenesis of Ovarian Teratomatous Teeth 

CHAPTER XIII 

Development of the Teeth in Pisces, Reptilia and Batrachia 312 

The Evolution of the Teeth in the Cod — In the Dog-fish — In the 
Crocodile — In the Lizard — In the Snake — In the Newt 

Appendix 327 

Note A. — On the Functions of the Cells of the Pulp — Note B. — 
Physiological (Lacunar) Absorption of the Alveolar Processes of 
the Jaws of Man 



PART I 

THE DENTAL TISSUES 




CHAPTER I 
PROLEGOMENA 

To write a book is to build a house. When completed, the 
chapters are the rooms, adroitly planned and suitably fur- 
nished with pictures of interest. From the windows, the eye 
surveys many well-known fields and oft- trodden paths; but, 
beyond, it is unable to pierce the problem hills of uncertainty. 

All literature relating to the theme of this thesis must, per- 
force, have its foundation stones laid on the classic work of 
Hunter, Kolliker, Owen, Tomes. It is impossible and unwise 
to ignore this work. In this manner the following pages are 
but comparable to a new wing of the house of Dental 
Anatomy, which these investigators have progressively and 
successfully raised; and if, from the windows, some instructive 
glimpses of the surrounding country can be obtained, and a 
few finger-posts pointing to the unknown, though by no 
means unknowable, be discovered by the eye — aided not by 
telescope, but by microscope, — then the author will rest 
content. 

That a treatise which deals chiefly with descriptions of the 
minute anatomy and pathology of the teeth and associated 
parts should be specially required may be questioned by 
some. Inasmuch, however, as these tissues, by reason of their 
unique constitution, differ most strikingly from other spe- 
cialised organs, such as the eye, the nose, the larynx; in- 
asmuch also, as general histological text-books treat somewhat 
sparingly, and sometimes incorrectly, of this subject, the 
production of these pages has seemed to the author perfectly 
justifiable, nay more, almost a necessity in these latter times. 
"Cut bono?" was once a frequent question; but there can be 
only few (if any) who would to-day care to diminish rather 
than to increase the range of knowledge, and limit the speciality 
of Dental Surgery to mere mechanical manipulations. 
3 



4 THE DENTAL TISSUES 

Dr. Otto Walkhoff, Professor of Conservative Dentistry in 
the University of Munich, in an introduction to his "Normal 
Histology of the Human Teeth," 1901, declares: 

"The special study of the Histology of the Teeth is the 
binding link between practical dental surgery and general 
surgery. The branch of learning which deals with this sub- 
ject is of great importance for the practical knowledge of the 
prospective dental surgeon. He learns not only the minute 
anatomy of the parts, but also the mutual relationships of 
those parts. Those dental surgeons who have had experience 
in making and examining sections of teeth are able to treat 
carious cavities with greater knowledge, and to appreciate 
and understand any complications that may arise, and there- 
fore take more appropriate and more therapeutic measures 
than those unaccustomed to the science. With the fuller 
education of dental surgeons in this study, the production of 
false pathological and other statements will be relegated to 
the past. Thus one acquainted with the structure of the tissues 
could never claim to completely cleanse and solidly fill the 
root-canals of teeth. A due regard to the Histology of the 
tissues of the mouth (as well as its Bacteriology), and the most 
perfect execution of mechanical operations form the ground- 
work of the conservative dentistry of later years." 

It must also be added, as has been expressed in another 
place, that the practice of microscopical work imparts to the 
student that delicacy of touch and nicety of adjustment of 
digital dexterity which is impossible of attainment by other 
means and methods. 

This book, then, is published with the avowed purpose 
of drawing the attention of the reader to the essentials of a 
profoundly fascinating branch of science; of indicating some 
■difficult and apparently irreconcilable and irresolvable histo- 
logical propositions; of attempting to elucidate, illuminate 
and complete other recondite and unfinished studies; and 
finally, of establishing upon a permanent and convincing 
basis many accepted postulates and uncontested facts. 

Dental Histology, with its collaterals, is nearly, but not 
quite, an inductive science. Unfortunately, it is by no means 



PROLEGOMENA 5 

an exact one, although, through the medium of new methods 
of research, there is no reason why, during the next half- 
century, it should not become so. 

The science and art peculiar to it are of paramount impor- 
tance alike to student, pathologist and surgeon. In the inter- 
pretation of many ordinary and extraordinary phenomena 
connected with the genesis and evolution of the teeth; in the 
solution of certain obscure physiological and anatomical and 
pathological problems; in the every-day diagnosis of oral 
and dental disease; in short, in the undoubted assistance it 
can and does render to the earnest worker in the art of Dental 
Surgery, it may fairly be claimed for this subject that to-day 
it cannot be dismissed without recognition, or without the 
bestowal upon its varied aspects of such thoughts and labour 
and research as they deserve. In its scope and aims it is 
certainly ancillary to no other branch of learning. 

On so slender a scaffolding it would seem somewhat difficult, 
if not well-nigh impossible, to build up such a large and 
diversified collection of valuable and interesting data; never- 
theless, a moment's reflection will soon assure the reader that 
this framework is extensive even in its limitations. 

To attempt to recall and record the History of Dental 
Histology would form a congenial and satisfactory task. 
Mere mention of the names of those specially associated 
with it must, however, here suffice. As for the past, it is 
pleasant to an Englishman to dwell on the works of Thomas 
Huxley, Sir Richard Owen, Salter, Sir John Tomes, Storer 
Bennett; while as for the present, the bibliography of British 
dental science has been enriched by the writings of C. S. 
Tomes, who has patiently and laboriously investigated, 
among other subjects, the development of the teeth of fishes, 
reptiles, batrachians, and marsupial mammals; of Howard 
Mummery, to whom our knowledge of the development and 
growth of dentine is largely due; of Milles and Underwood, 
in their researches on dental caries; of Leon Williams, the 
able and skilful exponent of the structure and pathology of 
human enamel; of Paul, who has successfully demonstrated 
the minute anatomy of Nasmyth's membrane; of J. G. 



THE DENTAL TISSUES 

Turner, who has identified himself with the etiology and pa- 
thology of dental cysts; and of Kenneth Goadby, the prolific 
contributor to current literature of a mass of information 
on dental and oral mycetology, etc. In America, the list of 
names must be headed by those of Andrews, Black, Norman 
Broomell, etc.; and on the Continent of Europe by those of 
Arkovy, von Ebner, Galippe, Grevers, Kolliker, Legros, Magi- 
tot, Miller, Retzius, Rose, Vignal, Walkhoff, Wedl, Weil, 
Zsigmondy, etc. 

Rising out of a review of this subject come many thoughts, 
and chief among them are the remarkable scantiness of actual 
and reliable information concerning many things. Thus, with 
regard to the normal minute anatomy of the hard tissues, no 
answers have been returned to the questions, "How is enamel 
fixed so intimately to the periphery of the dentine?" "Whence 
comes its pigmentation?" "What is the manner of develop- 
ment of the branches of the dentinal tubes?" As to the pulp 
and alveolo-dental periosteum, some knowledge is available 
of the nerve endings in the first, while the histology of the 
latter still remains, as far as its nervous system is concerned, 
a terra incognita. 

Turning to the realm of Pathology in general, and erosion 
of the teeth in particular, the causes of the occurrence of occlu- 
sion of the tubes requires further consideration, as do also the 
presence and sensitiveness or non-sensitiveness of the inter- 
globular spaces in hypoplasic teeth and ovarian cystic teeth, 
the changes in the dentinal tubes producing the "pipe-stem" 
appearance of caries, and their invisibility in senile affections. 
Tempting fields for research are all these and many others. 
The exigencies of this chapter disallow more than the brief 
consideration of one subject for discussion — viz., the pig- 
mentation of enamel. 

Thick sections of this tissue examined macroscopically before 
finally grinding, polishing and mounting always appear stained 

more or less deep brown colour. This is different from and 
other than that of the brown striae of Retzius. The thinnest 
sections ultimately reveal apparently but little, if any, pig- 
mentation. Is this colouring, then, due to mere optical effects? 



PROLEGOMENA 7 

In the opinion of the author, No. Because, examples of the 
natural staining of epithelial tissues constantly occur — as in 
the case of the epidermis of the negro, where granules of 
melanin are found in the rete Malpighii of the epithelial layer 
of cells. Other analogies may be cited also — e.g., the pigment 
corpuscles in the ramified nerve cells in the anterior cornua 
of the spinal cord of man, and the pigment bodies in the cortical 
substance of the hairs of man. 

Again, the normal pigmentation of the enamel is a prominent 
feature of the teeth of many rodents. This also disappears 
on grinding very thin; and it is impossible to say whether it 
is resident in the enamel rods, or in the cementing substance, 
or in both. The tissue is unequally pigmented; if it was due 
to the chromatic aberrations of light it would most likely be 
uniform. Finally, in the case of pathological or congenital 
pigmentation of the cementum and dentine, the colour, though 
pronounced in thick sections or even before these have been 
made, has vanished when the thinnest are examined. The 
inference would be that this may also hold good with regard 
to enamel. 

It would seem that the dental histologist of the future must 
more closely combine microscopical technics with a profounder 
knowledge of anatomy and physiology. 

Of the utmost importance to such an one are three great 
principles,- — the selection of material, the preparation of that 
material for experimental and histological research, and the 
correct interpretation of results. 

First, the selection of material which is about to form the 
basis of investigation must not only be confined to perfectly 
fresh tissues, but as far as it is possible to determine to tissues 
absolutely unaffected by morbid conditions. This may be 
exemplified by the study, say, of the histogenesis of the teeth 
in normal well-developed embryos and foetuses as compared 
with the different stages and rates of growth in rachitic indi- 
viduals of a corresponding age. Contrasting the appearance 
of the two conditions may throw useful light on both; but 
conclusions drawn from examination of diseased tissues errone- 
ously believed to be healthy, can only give rise to false deduc- 



8 THE DENTAL TISSUES 

tions and misleading statements. Loose plans of procedure 
unfortunately militate strongly against that advancement of the 
science which is so earnestly desired. 

Further, the preparation of the tissues is all important. 
The quotation of one single instance, in itself sufficiently 
striking, will be enough. The discovery of the real nature 
and characteristics of Nasmyth's membrane has followed the 
employment of proper methods of preparation. 

Thirdly, tissues having been properly selected and prepared, 
suitably stained and carefully mounted — the risk of shrinkage 
or swelling having been reduced to a minimum — must be 
scrutinizingly examined and carefully and critically inter- 
preted. It was undoubtedly the precipitation of amorphous 
silver chromate salts (as in Golgi's method of staining) or 
methylene-blue granules which lead Morgenstern and Romer 
to erroneously affirm the actual presence of amyelinic nerve 
fibres in the dentinal tubules and enamel. Check experiments 
must be conscientiously followed, and check stainings and 
methods of preparation adopted. 

In conclusion, the original worker must be assisted in his 
accurate explanations of the meanings of the structures of 
cells and organs by keeping himself quite en rapport with the 
latest teachings of physiology and pathology. He will be most 
helped by devoting his attention to a preliminary thorough 
study of the knowledge we possess of the differentiated func- 
tions of cells; of the general principles that underlie and 
govern the physiological methods of tissue formation; of the 
metabolism of the cells forming the component parts of that 
tissue; and of the effects of pathological influences on the life- 
histories of the cells and other essential elements of the organs 
with which he has to deal. 



CHAPTER II 
NASMYTH'S MEMBRANE 

Microscopical Elements: (i) Cellular layer; (ii) Translucent pellicle 
GENERAL CHARACTERISTICS 

Definition. — A macroscopically-invisible cellulo-laminar film 
situated on the free surface of the adult enamel of man and 
certain animals. 

Origin. — This tissue, which has recently been studied afresh 
microscopically, is now known to have its origin as an 
ectodermic formation of the epithelial cells of the enamel organ. 

It is most probable that the cellular layer is derived from 
the external epithelium, and the pellicle or innermost layer 
from the spent cells of the internal epithelium, which have 
previously undergone a keratinous or somewhat analogous 
change. 

With regard to its origin, R. R. Andrews ("The American 
Text-book of Operative Dentistry," p. 92, 1901), says that his 
investigations lead him to believe that the internal epithelium 
of the enamel-organ (ameloblasts) composes the cells of the 
membrane. These "having performed their function, have 
filled with calcoglobulin and have partially calcified, becoming 
somewhat like that tissue which we find on the borderland of 
calcification." That this is an entirely incorrect view is 
obvious when Paul's and the author's sections are examined. 

Distribution. — Situated externally on the cortical aspect of 
the unworn enamel of man, monkey and sheep, is found under 
suitable conditions Nasmyth's membrane. It is a thin con- 
tinuous tissue spread flat over the enamel, dipping into the 
naturally-formed pits and fissures on the surface, and limited 
in extent by the cervical portion of the tooth, to the edges of 
9 



IO THE DENTAL TISSUES 

which it is attached. Synonym. — The enamel cuticle. It has 
also been incorrectly termed "persistent dental capsule." 

Bodecker 1 considers that it is in direct union with the outer- 
most epithelial layer of the gum, being therefore the only 
layer which closes up the space between the neck of the tooth 
and the adjacent gum. 

In a well-developed adult premolar its measurements are 
29 mm. in its widest part, 19 mm. in the narrowest, and 26 mm. 
round the cervical region of the tooth. All teeth possess the 




Fig. 1. — Nasmyth's membrane attached to the eementum. Prepared by 
decalcification of a ground section. Magnified 40 times, p. The membrane; 
E. Enamel; D. Dentine; c. Cementum. 



membrane in a more or less complete condition. Even senile 
teeth when treated with a decalcifying solution to remove 
the enamel have traces of it, but it is best observed in those 
teeth which, while still unerupted (premolars, for instance), 
have been removed for the treatment of irregularities, because 
in this case the cellular layer is undamaged, though it may 
be injured during the act of extraction. Portions of the 
cellular layer may remain attached to the inner aspect of the 

1 "Anatomy and Pathology of the Teeth," p. 43, 1894. 



NASMYTH S MEMBRANE 1 1 

dental capsule, which as a rule comes away with the tooth. 
According to Kolliker it measures in thickness from i^ to 2/x. 
This is probably erroneous, a measurement of 50^ being likely 
to be more accurate. Easily detached by the action of strong 
acids, it is only when Paul's method of preparing specimens is 
adopted that its real normal structure is ascertained. 

HISTOLOGY 

Nasmyth's membrane consists of two parts (i) an outer 
cellular portion, and (ii) an inner structureless translucent 
lamina or pellicle. These are both intimately adherent, not 
only to each other, but also to the free ends of the underlying 
enamel columns. 

(i) The Cells 

The cellular portion is interesting, inasmuch as its structure 
is made up of a layer or layers of large polygonal flattened 
epithelial cells, with pronounced nuclei. "The epithelial cells," 
writes Bodecker {op. cit. p. 92), "in transverse section, have the 
appearance of shallow spindles. Not infrequently there occurs 
also a stratified epithelium on the surface of the tooth. The 
enamel-fibres are in connection with these epithelial bodies 
which, if detached, show delicate offshoots adhering in regular 
intervals— the broken enamel fibres. Sometimes the surface 
of the enamel is coated by a thin uniform layer of protoplasm 
with regularly scattered nuclei. In such an instance single 
epithelia are not traceable, though scarcely any doubt can arise 
about the epithelial nature of this layer." 

It is quite possible and most probable that the cells are 
more than one layer in depth. Preparations when correctly 
stained exhibit such a dense pattern of cells that this belief 
in the multiplicity of layers is probably well founded. It is 
doubtful, however, if more than three layers ever exist. The 
double or treble layers are not observed all over the surface 
of the pellicle, but only in those situations where the membrane 
dips down deeply into the pits or crevices of the enamel; and 
here too the pellicle itself is apparently thicker than elsewhere. 
The protoplasm of the cells is faintly granular. Under high 



THE DENTAL TISSUES 



powers, the spongioplasm and hyaloplasm may be clearly 
defined. 1 



tf* 







Fig. 2. — A piece of the thinnest portion of Nasmyth's membrane flattened 
out, and photographed from above. Its elastic nature made it impossible to 
critically focus it in all parts. Prepared by Paul's method. Magnified 200 
times, c. Nuclei of the cells; p. Translucent pellicle. 

1 The "spongioplasm," according to Schafer, is a reticulum or network of 
protoplasm in the cell substance; and "hyaloplasm" is the name applied to the 
material which occupies or fills its meshes. 



NASMYTH S MEMBRANE 1 3 

Paul 1 attributes to the cells an average diameter of 12m and 
a length of 25/x. Cells having "cogged" outlines — spiny 
cells — are seen constantly (Cf. Fig. 196) : and in places the 
polygonal cells are flattened, probably by mutual pressure, in 
one or more lateral directions, and may thus assume a cubical 
or even cylindrical shape. The nuclei are particularly large 
compared to the size of each cell, are ovoid in shape or nearly 
round in outline, and possess faint nucleoli. These are usually 
single, and often contain in their interiors, as well as near their 
exteriors, one or more vacuole-like, bright, shining globules. 

(ii) The Pellicle 

The inner or subepithelial layer is a delicate continuous 
membrane, apparently without histological structure of any 
kind. It is translucent, elastic and cornified, and resists the 
action of acids in a similar way to the sheaths of Neumann 
or the linings of Haversian canals. On its under surface, i.e., 
the part nearest enamel, a reticulated pattern can be fairly 
easily demonstrated. This corresponds to and is probably 
produced by the free ends of the enamel rods, which have 
left their hexagonal impressions on the membrane. It is to 
be noted that the hexagons of the pattern have sharp, clear 
margins made up of straight outlines, correspond in size to 
the diameter of the enamel rods, and in no way approximate 
the size of the epithelial cells which are "at least ten times 
too large for the enamel rods." (Paul.) 

In sections of Nasmyth's membrane which have been 
obtained in situ it has been possible to find in the deep enamel- 
pits lacunae similar to those of osseous tissue, surrounded by a 
capsule, and apparently associated very closely with the trans- 
lucent layer of the membrane. Tomes 2 has repeatedly seen 
this condition. How these encapsuled cells get into the pits 
or fissures is not quite clear. There is an occasional appear- 
ance noticed in teased or spread-out pieces of the membrane 
of the cells being arranged concentrically round certain tiny 
spaces, and it may be that these represent in some way the 

1 " Nasmyth's Membrane." The Denial Record, 1894. 
2 "A Manual of Dental Anatomy," p. 123, 1914. 



14 



THE DENTAL TISSUES 



spots where encapsuled lacunae may be deposited. A lacuna 
may perhaps represent a persistent retained and imprisoned 
cell of the stratum intermedium of the enamel organ where, 
owing to the formation of the cusps of the teeth, an involution 




Fig. 3. — A thicker portion of Nasmyth's membrane than in Fig. 2. Magni- 
fied 200 times, a. Hexagonal impressions of the enamel rods. 



of this layer of cells has taken place; or it may represent an 
aberrant osteoblast which has likewise remained unatrophied 
or unabsorbed. 

Prof. Rodolfo Erausquin of the University of Buenos Aires, 
in a private letter to the author, expresses the opinion which is 
very plausible, that the so-called "encapsuled lacunae" are, 
after all, merely vegetable cells introduced into the deep pits of 



NASMYTH S MEMBRANE 



15 




Fig. 4. — Enamel of a tooth, with Nasmyth's membrane on the free surface, 
removed from an oophoronic cyst or teratoma. Ground thin and then decal- 
cified. Unstained. Magnified 250 times. M. Nasmyth's membrane. 




Fig. 5. — Vegetable cells found in a pit on the surface of human Nasmyth's 
membrane. Photomicrograph supplied by Dr. R. Erausquin. 



1 6 THE DENTAL TISSUES 

enamel during the act of comminution of food, where they may 
be retained indefinitely. The accompanying photomicrograph 
adequately represents the microscopical appearances of such 
cells. 

Fresh research on this matter is needed before a dogmatic 
opinion can be expressed. 

It is now perfectly established that Nasmyth's membrane 
can be regarded with certainty as an epithelial remnant of 
the enamel organ, and thus the theories of Waldeyer, Rose, 
and others are to be considered correct. 

From the enamel of recent teeth removed from ovarian 
teratomatous cysts, the pellicle can be isolated by careful 
decalcification. 

It is absent, from the crowns of teeth found in follicular 
odontomes {q.v.), although, according to Warwick James, 
(''The Science and Practice of Dental Surgery," edited by 
Norman G. Bennett, 1914) this is not always the case. 



CHAPTER III 
THE ENAMEL 

Microscopical Elements: (i) Enamel rods and intercolumnar sub- 
stance; (ii) Curvatures of rods; (iii) Brown Striae of Retzius; (iv) 
Lines of Schreger; (v) Enamel "Spindles." 

GENERAL CHARACTERISTICS 

Definition. — The smooth, hard, glistening inorganic sub- 
stance which partially or wholly envelopes the crowns or visible 
portions of the calcified teeth of the Pisces, Rcptilia, and Mam- 
malia classes of the Vertebra ta. 

Origin. — It is the final product of the layer of cells — the 
ameloblasts — which constitute the internal epithelium of the 
enamel organ. It is yet undecided whether enamel is a secretion 
or conversion of these cells, but the balance of opinion would 
seem to be in favour of the former. 

Distribution. — Existing as (i) a tiny point or tip, as in the 
teeth of some members of the class Pisces, e.g., the order Ana- 
canthini — Merlucius vulgaris (the hake), the order Physos- 
tomi, family Muraenidae — Anguilla acutirostris (the eel) ; 
or (ii) a partial investment of the cutting edges of teeth, such 
as those of the incisors of Rodentia, the lower canines of some 
Biniodonts, &c; or (iii) longitudinal bands, as in the upper 
canines (tusks) of the wild boar; or (iv) an entire cap of varying 
thickness, which covers over the normally erupted parts of the 
teeth of mammalia generally, — except of the sub-order Artio- 
dactyla, where a thick coating of cementum is developed 
in this situation, — enamel is the hardest tissue of the teeth 
or any of the organs of man and animals. 1 

1 In the mandibular incisors of the Chiromydce (e.g., the Aye Aye) enamel 
forms by far the greater portion of the teeth, exceeding in amount both dentine 
and cementum. 



iS 



THE DENTAL TISSUES 



In man it intervenes between the translucent pellicle of 
Nasmyth's membrane, placed externally, and the periphery 
of the dentine which goes to make up the greater part of the 
tooth substance internally. Nasmyth's membrane is invisible 
macroscopically; at least it is unrecognisable, and, therefore, 
as this film becomes abraded the enamel becomes the most 
external of the dental tissues. 

In the Artiodactyla it occupies a position (Fig. 6) between 
the cementum and the dentine. 




Fig. 6. — Vertical section of a molar of a young horse. Section ground thin. 
Unstained. Magnified 45 times, e. Enamel; d. Dentine; c. Cementum. 

In sagittal (vertical labio-lingual) sections of the well- 
developed incisor teeth of man. unworn by attrition, it measures 
at the incisive edge about 2 mm. in depth; and then, as it 
gradually approaches the cervical margin, it becomes thinned 
down to zero. Over the cusps of premolars it is 2.3 mm., and 
over the cusps of molars it is 2.6 mm. in thickness. 

The enamel of the deciduous teeth may be half the thickness 
of that of the permanent series. 

At the gingival edge it may or may not slightly overlap the 



THE ENAMEL 



19 



thin structureless border of cementum. Monsieur Jules 
Choquet, who investigated (1899) the question of the anatom- 
ical relationships of the two tissues, in an interesting brochure 




Fig. 7. 





Figs. 7, 8, 9, and 10. — Adapted fror 
and published by L'Odonlologie, 18c 
Enamel; c. Cementum; d. Dentine. 



photomicrographs by Jules Choquet, 
). Semi-diagrammatic. Human, e. 



entitled "Note sur les rapports anatomiques existant chez 
l'homme entre l'email et le cement," has succeeded in throw- 
ing light on this subject. He examined and reported on 
twenty-nine human teeth; and found that the enamel covered 



THE DENTAL TISSUES 



the edge of cementum eight times (Fig. 9) , while the cementum 
overlapped the enamel seven times (Fig. 8). This author also 
reports that, in the majority of cases, the enamel and cementum 
meet each other, and there is no overlapping (Fig. 7). Out of 
his twenty-nine sections this occurred nineteen times. Thus 
the rule would be that the two tissues are in absolute contact, 
and both lie in the same plane without any involution what- 
soever. Choquet further found that in 27.5 per cent, of the 
cases he examined, there was a breach of continuity of these 
two structures, leaving a minute portion of the dentine fully 
exposed (Fig. 10). His sections were cut longitudinally, 




-Vertical section of 
diagrammatic. 



Human tooth, from a photomicrograph. 
Enamel; d. Dentine; c. Cementum. 



and some were studied on both their aspects, whilst others 
only on one. "Cette difference tient a ce que dans certains 
cas il y avait eu fracture de l'email d'un des bords pendant 
l'usure de la coupe." There was often a diversity of method 
of ending of the tissues: thus, one section would have on its 
labial aspect the enamel overlapping the cementum, and on its 
lingual surface, the former internal to the latter. The teeth were 
representative specimens from young, old, and gouty subjects. 
This subject has been re-examined by Thorsen {Den Norske 
Tandlaege Tidende, 191 7,) who finds that enamel meets 
cementum edge to edge in 30 per cent, of cases; is covered by 
cementum in 60 to 65 per cent., and covers cementum in 0.5 



THE ENAMEL 21 

per cent. In 5 to 10 per cent, the two tissues were not in 
contact. 

On rare occasions, as in Fig. 11, from a section in the pos- 
session of Sydney Spokes, the margin of cementum may extend 
in a remarkable way, some considerable distance over the edge 
of enamel. From the structure of the tissue, consisting as it 
did of matrix containing many large lacunas and incremental 
lines, it is important to point out the fact that the cementum 
was in no sense normal. The tooth, a mandibular third molar, 
was slowly erupting in an irregular manner. 

Macroscopical Appearances. — Surface smooth, shiny, some- 
times traversed by tiny vertical or horizontal depressions, 
occasionally scrobiculated and normally deeply fissured in 
premolars and molars, and pure white in colour. When 
fractured, pure white, non-lustrous. 

HISTOLOGY 

On microscopical examination Human enamel reveals many 
interesting structures. These may be described in the order 
of their importance as: (i) The striated columns and calcified 
matrix; (ii) The curvatures or courses of the rods; (hi) The 
brown striae of Retzius; (iv) The lines of Schreger; and, (v) 
Certain spaces or "enamel spindles." 

(i) Enamel Rods (Man) 

Enamel is built up of minute solid calcified columns or rods, 
frequently hexagonal or pentagonal in shape, all united by a 
matrix or intercolumnar cementing material of somewhat 
different refractive index. 1 It is probable that the real shape 

1 It is extremely difficult to estimate the chemical composition of enamel. 
Hoppe-Seyler (Handbuch d. Physiolog. und Pathologisch-chem. Analyse, 1893) 
has the following formula: Cai CO 3 (P0 4 )e. 95-35 per cent.; MgHPO*, 1.05 
per cent, and so-called "organic substance," 3.60 per cent.; while Dr. Lovatt 
Evans (Proc. Internet. Med. Congress, 1913) thinks that in dried enamel of 
man the organic material amounts to 1 per cent, or 2 per cent., for he com- 
puted that 3.659 gm. contained 39.56 c.c. of gas consisting of carbon dioxide 
30.21 c.c, and nitrogen 9.35 c.c. 

The "organic substance," and "organic material" mentioned above are 
probably, as Tomes has shown, (Denial Anatomy, 1914, p. 34), only water com- 
bined with the lime salts. 



THE DENTAL TISSUES 



of the columns is that of a solid cylinder. If an ameloblast 
could undergo complete segregation and continue its functional 




Fig. 12. — Sagittal section of the incisive edge of a Human incisor tooth. 
Ground thin. Unstained. Magnified 45 times. Shows the general pigmented 
appearance of the enamel, e. Enamel; d. Dentine. 



activity a rounded rod would, no doubt, result. The hexagons 
are most likely produced by the lateral pressure of lengths of 



THE ENAMEL 



23 



contiguous rods, in much the same way as obtains in the 
six-sided cells of the bee's honey-comb (See Fig. 15). The 




Fig. 13. — Sagittal section of the incisive edge of a Human canine tooth. Ground 
thin. Unstained. Magnified 45 times, e. Enamel; d. Dentine. 

matrix is not a connective tissue ground substance; but merely 
a more or less perfectly calcified cementing substance. 



24 



THE DENTAL TISSUES 




Fig. 14 — Human enamel. Prepared by grinding. Unstained. Magnified 
250 times. 




Fig. 15. — Enamel rods, as seen in transverse section. Decalcified and teased 
out. Magnified 500 times. 



THE ENAMEL 



25 



When isolated by means of the careful application of dilute 
acid solutions, the rods have their cementing substance dis- 
solved and can then be examined critically (Fig. 16). They are 
absolutely solid in the adult or mature state, i.e., when fully 
completed, rather flexuous or curved in contour, and measure 
.005 mm. (5/i) in diameter. Kolliker in "A Manual of Human 
Microscopic Anatomy," i860, gives their breadth as 6.4/x to 
5.IM. Their length may attain to 2 mm. The outlines of 




section of enamel rods, magnified 2,000 times. 
Photomicrograph by Leon Williams. 



the rods, in addition to being curved, are beaded, or very 
slightly varicose. Their long axes are, speaking broadly, placed 
at right angles to the surface of the tooth. Their inner ex- 
tremities are inserted securely in tiny hexagonal depressions 
on the surface of the dentine: while their outer ends are free, 
and crop out of the periphery of the enamel itself, thus giving 
rise to imbrication lines on its cortical outer aspect, and probably 
affording close attachment to the pellicle of the enamel cuticle, 
to the hexagonal impressions of which they are ultimately and 
intimately fixed (see Fig. 3). 



26 



THE DENTAL TISSUES 



The '''term "imbrication lines" has been introduced by Prof. 
Pickerill of the University of Otago, New Zealand, ("The Pre- 
vention of Dental Caries and Oral Sepsis," 191 2), to describe 
these outcrops on the surface of enamel of the free ends of 
the rods. He has clearly demonstrated the fact that, to a 
slight extent, the ridges and furrows of the enamel periphery 




Fig. 17. — Section of enamel from Human tooth. Magnified 2,000 times. 
Dark ground illumination. Foeussed in the middle of the section to show the 
granular calcified plasm-strings. The transparency of the cement-substance 
between the enamel rods is perfectly demonstrated in this illustration. Photo- 
micrograph by Leon Williams. 

are made up of the overlapping free terminations of the rods. 
Inasmuch as this arrangement resembles that which obtains 
generally in the disposition of the scales of a fish, or the tiles of 
a house roof, the term is very appropriate. 

At regular linear intervals, and at distances varying from 
5m to 3. 5m, the enamel rods are crossed by distinct shadings 



THE ENAMEL 27 

called transverse striae or varicosities, which closely resemble 
the stripes of striated voluntary muscle fibres (Figs. 18 and 23). 
These striae are only seen in longitudinal or oblique sections 
of the rods, and are ordinarily very faint. They are rendered 
more apparent by the action of dilute hydrochloric acid, and 




Fig. 18. — Section of enamel from Human tooth. Magnified 350 times. 
Section prepared by Howard Mummery. The transverse markings of the 
enamel-rods are very pronounced. The enamel-rods are everywhere seen to be 
united by projecting processes. Photomicrograph by Leon Williams. 

occasionally when a }-i per cent, solution of chromic acid has 
been used. The markings are more clearly and easily seen in 
the outer portions of the enamel, and may be remarkably 
demonstrated in very pigmented or degenerated conditions of 
the hard tissues: they may be very indistinct, or even absent, 
in the region of the enamel near the dentine. 



2 8 



THE DENTAL TISSUES 



According to Bodecker the enamel is traversed by fibres of 
living matter located in the interstices between the enamel rods. 
The fibres are connected with one another by delicate fibrillae, 
piercing the enamel rods in a vertical direction. Besides these 
rectangular unions, the basis-substance contains a minute net- 
work of living material which pervades it throughout its whole 
extent. The enamel fibres send conical thorns toward the 





Fig. 19. Fig. 20. 

Fig. 19. — Transverse section of enamel, after Bodecker. Magnified 2,000 
times, e.r. Rods of enamel, partly exhibiting formations like nuclei; the light 
interstices between the rods traversed by delicate beaded fibres; e.f. or by 
vertical thorns. 

Fig. 20. — Longitudinal section of enamel and dentine, after Bodecker. 
Magnified 1,200 times. E.R. Enamel rod; e.f. Enamel fibre; D. Dentine; D.F. 
Dentine fibrils; p. Soft protoplasmic formations at the boundary between both 
tissues. 



enamel rods, and such thorns are visible in all interstices 
between the enamel rods. 

The enamel fibres are continuous on the outer surface with 
the covering layer of flat epithelium, and on the inner surface 
with the dentinal fibres. The connection with the latter is 
either direct or indirect through a network of living matter, or 
through intervening protoplasmic bodies in the interzonal layer 
(Fig. 19). 

And also Abbott {op. cit. p. 95) has further given a drawing 



THE ENAMEL 2Q 

showing the enamel-rods, the light reticulum within them, the 
intervening fibres, and the lateral off-shoots of the fibres. 

The researches of Tomes, Leon Williams, and others, have, 
however, demonstrated the fallacy of such statements, and it 
must surely be an unpardonable hyperbole to affirm the exist- 
ence of a chain of living material passing from the periphery 
of a tooth to its sentient pulp. The experiments of Tomes and 
Black have conclusively and for ever proved the inorganic 
nature of enamel. 




Fig. 21. — Vertical section of normal enamel treated by Golgi's rapid process. 
Magnified 45 times. 

Nearly every section of normal as well as pathological enamel, 
whether ground and mounted in balsam or glycerine, whether 
stained or unstained, whether decalcified slightly with weak 
acid, like one per cent, citric acid, or prepared under conditions 
resembling Nature as closely as possible, reveals a certain 
degree of pigmentation. If, however, treated with Golgi's 
rapid silver chromate method, this coloration in normal ground 
sections is intensified. 

The enamel of ovarian teeth, deciduous teeth, and nodules 
found on the necks or roots of teeth, exhibits also the 
pigmentation. 



AO 



THE DENTAL TISSUES 




Fig. 22. — Longitudinal section of enamel from outer surface of Human in- 
cisor. Magnified 3,000 times. The structure of the calcined enamel-globules 
of which the rods are composed is very finely shown in this illustration. This 
section represents normal human enamel of the finest type. Photomicrograph 
by Leon Williams. 



THE ENAMEL 



31 



Of all investigators in the difficult subject of enamel his- 
tology, the name of Leon Williams will ever stand out pre- 
eminently. His magnificent work on the minute anatomy 
as well as the pathology of this tissue is well known, and he 
has contributed probably by far the greatest amount of knowl- 
edge on the matter. 




Fig. 23. — Longitudinal section of enamel from Human tooth. Magnified 
1,000 times. Shows enamel-rods passing through Retzius bands without break 
of continuity. The rods are separated by rather more than the normal amount 
of cement-substance, and show imperfect formation in lower right-hand corner. 
Photomicrograph by Leon Williams. 

According to this author 1 enamel rods are constructed by 
the successive deposition of certain "bodies" formed in the 
enamel cells, a deposition which goes on with the utmost order 
and regularity. The rods possess a more or less definite 

1 "On the Formation and Structure of Dental Enamel." The Dental Cosmos, 
1896. 



32 THE DENTAL TISSUES 

organisation. These "bodies" are beads of granular material, 
which, under high magnification, are joined together by calci- 
fied plasmic strings and processes (Figs. 17 and 22). They 
lie exactly opposite each other, and the granular strings are 
larger and more clearly defined on the extreme margins of the 
enamel rods. Thus Leon Williams has demonstrated indubi- 
tably that the "bodies" are connected vertically by plasmic 
strings of granular origin which traverse the entire length of 
the rods; that they are also united to the bodies of con- 
tiguous rods by radiating processes, or even touch one another at 
the points of the greatest diameter of the rods; that there may 
be as many as fifteen or twenty calcified plasmic strings in 
each enamel rod; and that their ultimate structure is most 
suitably revealed by the action of weak acids, such as citric 
in lemon juice, which first removes the connecting threads. 

The Cementing substance or matrix varies considerably in 
amount. In the majority of cases, in the teeth of man, the 
rods are more or less in actual contact throughout their 
entire course, being united by the varicosities or bodies: but 
in some sections they lie quite apart, separated sometimes by 
matrix which may equal one-fourth or one-fifth the diameter of 
a column (viz., iju), (Fig. 16). This translucent intercol- 
umnar, calcified substance has in it delicate connecting lateral 
processes and fine, tiny granules, and does not contain either 
the organic fibres, which Bodecker 1 and Abbott 2 affirm pass 
between the rods and give off "thorn-like" processes, or the 
channels which have been described by von Ebner 3 (Fig. 19). 

Otto Walkhoff, 4 ex cathedra, refuses to grant that this cement 
substance exists. He examined the enamel rods of certain 
Primates, Camivora and Ungulata, in which the structural 
elements of the tissue are regular. He affirmed that vertical 
sections of enamel never give, for great distances, the con- 

1 "The Anatomy and Pathology of the Teeth," 1894. 

2 "Minute Anatomy of the Human Tooth" in Trans. Dent. Soc., New York, 
1882. 

2 " Histologic der Zahne" in "Handbuch der Zahnheilkunde," 1801. 

4 "Contributions relating to the more minute structure of the Enamel, and to 
the Development of Dentine." Deutsche Monalsschrift fur Zahnheilkunde, 
Jan., 1898. 



THE ENAMEL 33 

tours of the rods in one plane, and that observations on 
such sections are untrustworthy. When magnified 3,500 
times, a measurable, thick, doubly coloured stripe was seen: 
viewed horizontally, the rods, at a magnification of 2,400, 
exhibited no cement substance. He wrote: "A series of 
photomicrographs with the apochromatic 1.9 mm. oil immer- 
sion, objective N.A. 1.40, showed that enamel rods consist 
of two parts optically distinctly divided from each ^other. 
The central part, or real body of the rod, is grainless, or, at the 
most, slightly spotted, but darker coloured than the pe- 
ripheral layer, which appears whitish. A delicate, somewhat 
darker line forms the border between the two layers; the outer 
border lining the whole column, which appears somewhat blacker, 
is sharply sectioned, even with high magnifications. Such 
pictures are produced only when focussing has been most 
exact, and where possible has been directed to the surface of 
the rod. In its surroundings there are immediately seen, if 
there is the slightest obliqueness in the section, diffraction 
seams, especially if oblique illumination has been used. With 
inexact focussing the picture totally changes. Between the rods 
there is then shown a line which appears dark, which by increas- 
ing the inexactness grows in width. What previously was light 
now becomes dark, and such a picture gives only too well the 
delusion of cement substance between the enamel rods." 

A recurrence to the belief in the existence of an organic 
matrix in the structure of enamel has been furnished in the 
pages of the Deutsche Monatsschrift fur Zahnheilkunde, August, 
1902, by Viggo Andresen of Vejle, Denmark. His paper 
("Beitrag zur Histologic des Schmelzes") is, however, in- 
conclusive, and his illustrations unconvincing. 

It is interesting to note the various opinions and theories in 
connection with the histology of enamel and its rods. 
Thus: 

Abbott says that "normal enamel is non-striated." 

Sudduth 1 denies that the rods have any internal structure. 

von Ebner believes in the existence of the striae but considers 
they are an artificial appearance, due to the action of acids. 

1 "Dental Embryology and Histology" in "American System of Dentistry," 



34 THE DENTAL TISSUES 

The propositions advanced as to the origin of the shadings or 
transverse markings are: 

(i) An intermittent calcification of the rods would produce 

the dark and light bands. (Hertz.) 
(ii) They are due to the existence of beads or varicosities in 

the rods. (Kolliker, Waldeyer, Haycraft, Ewald, and 

Leon Williams.), 
(iii) Or to inequalities on the surfaces of the rods. (Sud- 

duth and Febiger.) 

(ii) The Courses or Curvatures of the Rods 

Individually each rod runs a more or less spiral course 
and often, decussates with its neighbours, so that it is 
exceedingly difficult, if not impossible, to trace its entire 
course. 

Collectively, the courses are neither perfectly straight nor 
perfectly parallel. At the cervical region they run horizon- 
tally outwards from the dentine; at the cutting edge or the 
masticating surface they are chiefly set vertically with it. 
They thus radiate outwards all round. According to Tomes, 
"Dental Anatomy," 1914, p. 40, "On the whole the rods are 
parallel and run from the surface of the dentine continuously 
to that of the enamel. Their paths are not, however, either 
perfectly straight or perfectly parallel; for alternate layers 
appear to be inclined in opposite directions, while they are also 
wavy, forming several curves in their length. The curvature 
of the rods is most marked on the masticating surface: while 
the layers, alternating in the direction of their inclination, 
as just described, are in places transverse to the long axis of 
the crown, and correspond to the fine imbrication lines on the 
surface of the enamel, which appear to be caused by their 
outcrop. The curvatures take place in more than one plane; 
in other words, the course of the individual rod is more or 
less a spiral." 

A general idea of the courses of the rods may be obtained 
by macroscopic examination of a section. 



THE ENAMEL 



35 



(iii) The Brown Stria of Retzius 

Nearly every longitudinal section of enamel exhibits in a 
more or less degree these stripes. They appear as shadings 








Fig. 24. — Vertical section of Human enamel. Unstained, and non-decal- 
cified. Magnified 250 times. The lines which run across the rods are cracks 
in the tissue produced by grinding the section. 

or brown markings, arranged in the form of arcuate stripes; 
and they maintain a certain amount of parallelism to the 



36 



THE DENTAL TISSUES 



boundary-line of enamel and dentine, which may be called the 
amelo-dentinal junction (Fig. 25). Crossing the columns in 
various planes and in various directions, they are more pro- 
nounced on the cortical portions of the tissue, but extend right 
up to the junction. Between thirty-six and forty have been 
counted as crossing a segment of enamel, but the number varies 
very greatly. The bands are interrupted partially or com- 




Fig. 25. — The Brown Striae of Retzius in enamel. Prepared by grinding thin. 
Unstained. Magnified 40 times, e. Enamel; d. Dentine. , 

pletely. Sudduth calls them "the broken striae," etc. Many 
are broad and many are narrow, the thickest and most marked 
of the former measuring sometimes, roughly, one-fifteenth part 
of the whole thickness of the enamel. These stratifications 
are only visible in vertical sections. Horizontally, the stripes 
are cut obliquely or transversely, and thus are seen as concen- 
tric bands, darker and more distinct at the edge than near the 
dentine; and therefore they give the enamel a more or less 
lamellated appearance. 

The striae of Retzius are due to pigmentary deposition in the 
rods. The theories propounded by von Ebner and Kolliker 



THE ENAMEL 37 

have been dismissed by Leon Williams as incorrect. The 
former observer supposes that the bands are due to "imprisoned 
air or gas which has entered the ground-off ends of the rods 
through minute channels." And to this Leon Williams replies 
{op. cit. page 475) that the idea is a mistaken one, "first, 
because the supposed canals have no existence; secondly, be- 
cause the ground-off ends of enamel rods do not appear except 
when the section of enamel is ground at a certain angle." 

According to Walkhoff (loc. cit.) the stria? of Retzius are 
nothing else than the ordinary transverse striping of the enamel 
rods on a large scale. He declares that both striae are the 
expression of the deposition by the lime salts of the enamel- 
tissue strata-wise, a longer lasting interruption of the calcifying 
process producing the Retzian stripes, and one short, often- 
repeated, the transverse striae of the prisms. 

Thus the brown striae of Retzius have been attributed in 
their origin to: — 

(i) The lamella ted mode of formation of the enamel; 

(Kolliker, Walkhoff.) 
(ii) The entrance of air into cavities between enamel rods; 

(von Ebner.) 
(iii) The varying character of food taken by the mother 
during the period of gestation, some food being rich in 
lime salts of one kind and some rich in salts of 
another kind; ("American System of Dentistry," p. 
656, 1887.) 
(iv) And finally, and correctly, pigmentation. (Leon 
Williams.) 

(iv) The Lines of Schreger 

By reflected light, as well as by transmitted light, it is often 
possible to distinguish in ground perpendicular sections of 
the teeth of man, entire band-shaped layers of rods alter- 
nately decussating in such a manner as to produce lines. By 
the former, they appear white, by the latter black, as in the 
photomicrograph. These differ very markedly from the striae 
of Retzius, inasmuch as they run transversely to them (Fig. 26) 



38 



THE DENTAL TISSUES 




Fig. 26. — Vertical section of Human enamel shewing the lines of Schreger. 
Section ground thin. Unstained. Magnified 45 times, e. Free surface of the 
enamel; s. Schreger's lines; d. Dentine. 




THE ENAMEL 



39 



and are long, level, very broad bands, which bear some resem- 
blance to flat clouds (Fig. 28) of the cumulo-stratus type. 
All|sections by no means exhibit them; but those specimens 
which do, commonly shew them most clearly and distinctly. 
They blend together, and therefore form blackish masses in the 
enamel. They may be distributed anywhere throughout the 
thickness of the tissue, but very often are confined to its 
inner aspect, particularly at the cusps of premolars and molars. 




Fig. 28. — Schreger's lines in enamel, as cloud-like masses through dense 
pigmentation. Magnified 300 times, s. Schreger's lines; d. Dentine with 
enamel spindles. 

High powers reveal the fact that the rods are histologically 
normal, and it is only low magnifications which make apparent 
their occasional lengthwise groupings. 

(v) Certain Spaces or "Enamel Spindles" 

Independent of certain cavities or clefts on the free surface 
of enamel, which have no special structure, there can often 
be found in teeth free from any apparent structural defects, 
near the amelo-dentinal junction, irregularly shaped chasms, 
which in ground sections are remarkably clear and brilliant 
(see Fig. 31). They appear to be in direct continuity with 



40 



THE DENTAL TISSUES 




Fig. 29. 




Fig. 30. 

Figs. 29 and 30. — Vertical sections through cusps of H 
with Golgi's rapid process. Magnified 45 times, e. 
f. Fissure with clear structureless margins. 



uman molar. Stained 
Enamel; d. Dentine; 



THE ENAMEL 



41 



those few dentinal tubes which manage to cross the boundary 
line of the two hard tissues. In fact they resemble bulbous 
enlargements of the tubes (Fig. 32). Situated between the rods, 
in the cement substance, which, according to von Ebner, and 
quoted by Romer in his "Zahnhistologische Studie," 1899, 
p. 39, is more abundant near the dentine than the cortex, 
they run vertically outwards, are narrow, and about 40JU long. 
They may be clubbed or spindle-shaped. 




Fig. 31. — Vertical section through cusps of tooth. Magnified 50 times. 
e. Enamel; d. Dentine, many tubes of which end in the enamel spindles. 
Photomicrograph by Douglas Gabell. 



These spaces are not infrequently observed in vertical ground 
sections of molars or premolars. 

In the margins of the apices of the dentine cusps (Fig. 33) 
they are more numerous than in the saddle-shaped depressions 
between them, in which situation they are only to be met 
with singly or in sparse numbers. The knobs sit on the den- 
tinal tubules exactly like ears on the stems of the straw of 
corn bound up into sheaves. Those found in the highest 
parts of the cusps appear to stand upright; while on the con- 



A 2 



THE DENTAL TISSUES 





Fig. 



33- 



Figs. 32 and 33.- — Adapted from two drawings by Kretz, in Romer's 
" Zahnhistologische Studie," 1899. Fig. 32. — Vertical section through amelo- 
dentinal junction in molar of a child, stained with gold chloride, and potassium 
iodide. Magnified 1,500 times, d. Dentine; e. Enamel; T. Dentinal tube; 
K. Enamel spindle; c. Dark red corpuscle in the interior of the enamel spindle. 
Fig. 33. — Vertical section through the amelo-dentinal junction of a cusp of a 
left maxillary first molar of a boy, aged 13 years. Stained as in last Figure. 
Magnified 250 times, e. Enamel; d. Dentine; k. Enamel spindles. 



THE ENAMEL 43 

trary those at the slopes incline more or less to the horizontal 
plane. Thus, in a longitudinal ground section through the 
middle of the cusp they are cut perpendicularly, whereas in a 
tangential ground section going through the lower portion 
they are found for the most part cut transversely. 

In sections ground in the ordinary way, and subsequently 
treated in the usual manner, these enamel-knobs stand out 
black or dark grey on a light background. There is no internal 
structure visible, the space being filled with detritus, etc., 
from the act of grinding. 

Whether protoplasm ever filled them is a difficult matter to 
decide. It is probable that in the fresh condition it did. 

Various accounts are given by different authors as to their 
histological characteristics, amongst whom Tomes, von Ebner, 1 
Hollander, 2 Wedl, 3 Bodecker, 4 and Oscar Romer 5 may be cited. 

Charles Tomes {op. cit. p. 49) makes no mention of their 
contents, and concludes that "perhaps they are to be regarded 
as pathological." 

That hollow spaces constitute these enamel-spindles von 
Ebner and Wedl are agreed: but the former holds that they 
contain air, and the latter that they are filled with amorphous 
dark calcareous masses, von Ebner thinks they are actually 
produced by the shrivelling up of the cement substance, which 
is more easily possible at the amelo-dentinal line than at the 
free surface of the tissue. Hollander describes their presence 
in the juxta-dentinal zone of enamel, but regards them as non- 
pathological. Bodecker says "They invariably contain proto- 
plasmic bodies of distinctly reticular structure and sometimes 
one or more compact clusters, which may be spoken of as nuclei. 
The spindle-shaped corpuscles stand at their central terminations 
in direct connection with the ends of the dentinal fibres, as 
these originated from repeated branchings. At many places, 
especially those corresponding to the crown apices, the spindle- 
shaped enlargements of the dentinal fibres are very numerous, 

1 SchefT's " Handbuch der Zahnheilkunde," Vienna, 1891. 

2 " Die Anatomie der Zahne des Menschen und der Wirbelthiere," Berlin, 1877. 

3 "Pathologie der Zahne," Leipzig, 1870. 

4 Heitzmann's "Mikroscopische Morphologie," Vienna, 1883. 

6 N erven in Zahnbein, "Zahnhistologische Studie," Freiburg, 1899. 



44 



THE DENTAL TISSUES 



and nearly regular in size and direction In the teeth 

of younger persons the spindle-shaped swellings are relatively 
larger and more regular than in those of older people." This 
is called the "Bio-plasson theory." 

Romer coincides on the whole with Bodecker's view, with 
the reservation that he would apply the term "dentinal 
tubules," instead of "dentinal fibres," to those formations 
which widen out into clubs or spindles in the enamel. He 
declares that the spaces contain an organic matter capable 




Fig. 34. — Vertical section through the coronal part of a tooth. Prepared by 
Weil's process. Magnified 250 times, e. Enamel; d. Dentine; e.s. Enamel 
spindle critically focussed to shew Romer's corpuscles. 

of becoming stained with chloride of gold, and appear of a 
reddish tint, varying from a rose-colour to a dark-red hue 
(marked C in Fig. 32). He admits that in most cases they 
are merely filled with air, through the shrinking of some of 
the organic material; but affirms that when teeth are treated 
by the Koch-Weil method there is no shrinkage, and that a 
non-reticulated organic substance is really present inside the 
knob. He describes and figures (Fig. xxxiii., Tafel vii.) in one 
space "several spherical corpuscles hanging together by a fine, 



THE ENAMEL 45 

scarcely measurable fibre, also stained dark-red and running 
out into a fine point" (see Fig. 32, also Fig. 34). In conclusion, 
he writes: — "I should not, however, call these round or oval 
corpuscles cell-nuclei, as Bodecker does; especially I cannot, 
like him, in defending his 'Bio-plasson' theory, testify to a 
connection between these knobs and 'the living enamel 
material ; ' but I think we should much rather venture to see in 
these fine corpuscles, so often arranged in rosary-like order, 
sensitive nerve-end apparatus of the nerve filaments which run 
in the dentinal tubules." For the arguments which Romer 
advances in favour of this extraordinary hypothesis, see his 
paper. 

The tubes of the dentine themselves often traverse the 
boundary line and penetrate the enamel sometimes to a depth 
of 30M. They run in the cement substance, not in the interior 
of the rods. 

Before altogether dismissing these theories, one or two more 
instances may be given of other opinions on this most interest- 
ing subject. 

F. T. Paul (The Dental Record, p. 495, 1896) explains their 
occurrence in this manner : — "In early mammalian tooth- 
germs, the ameloblasts and odontoblasts are seen to be sepa- 
rated by a thin band of transparent dentine matrix, due to 
certain changes in the surface of the pulp. This band has 
two sets of processes of formed matrix. One, as Howard 
Mummery first showed, passes between the odontoblasts to 
communicate with the connective tissue matrix of the pulp, and 
the other extends outwards between the ameloblasts, which, 
in some instances, are therefore kept apart, and thus form 
elongated spaces filled with the imperfectly calcified matrix 
of dentine. 'That processes of dentine matrix thrust up 
between the enamel rods should never calcify, is certainly 
nothing surprising when one remembers that the first layer 
of dentine usually only calcifies imperfectly, being character- 
istically the site of the interglobular spaces of Tomes.' " 

Waldeyer (in Strieker's "Handbuch der Lehre von den 
Geweben," Leipzig, 187 1) denies that the spindle-shaped spaces 
in enamel exist at all, as structural elements, either as develop- 



46 THE DENTAL TISSUES 

mental errors or pathological lesions. He bases his view on the 
assumption that the least defect in the parallelism of the sections 
would be likely to lead to incorrect appearances. Cracks or 
fissures in the enamel, produced by manipulative interference, 
would also yield deceptive results. Hertz, too, another of the 
earlier investigators, interpreted the meaning of these spaces 
in a similar way. 

But Walkhoff 1 has often seen them. 

One of the most difficult problems in the whole of dental 
histology is that connected with the relationship of enamel 
and dentine; for not only is it hard to conceive how enamel, 
an ectodermic substance, should be so securely fixed on the 
surface of a mesodermic substance, and by what, means they are 
thus bound together; but the transpiercing of the amelo- 
dentinal boundary by the dentinal tubes is infinitely still more 
perplexing. Walkhoff has published {op. cit.) an ingenious 
hypothesis in attempting to explain this phenomenon. In 
common with Wedl {op. cit.) and von Ebner, he assumes that 
at this border-line there must have been an absorption of the 
first deposited dentine. His arguments in favour of this are 
founded on the facts that under the enamel, Tomes' granular 
layer is never seen, because, though once existing, it has in the 
process of time become absorbed: that the dentinal canals 
run up to the edge without much narrowing of their diameters, 
thus apparently proving that they have been diminished in 
length: and, finally, that here, too, there are practically no 
branchings, these having disappeared in consequence of the 
resorptive process. 

Granting that the interpretations of these phenomena are 
correct, he proceeds to explain that, owing to an especial 
vitality on the part of certain individual tubes, they are enabled 
to completely resist the absorption of the defectively built 
dentine which is going on all round, remain in situ, and, there- 
fore, have the appearance of actually projecting beyond the 
amelo-dentinal junction. Walkhoff adds that the canals appear 
as if sharply cut off, a proof that their terminations are absorbed. 

1 Deutsche Monatsschrift }iir Zahnhcilkunde, January, 1898; also "Die Normale 
Histologic Menschlicher Zahne," Leipzig, 1901. 



THE ENAMEL 



47 



The direction of their courses is not always parallel with the 
enamel columns, because they frequently break through the 
rods transversely. There occur formations (the enamel-knobs) 
at the apices of the dentine cusps in the teeth of Primates and 
Carnivora, which may reach far into the enamel, and do not 
consist of simple dentine tubes, but may have round them a 
large amount of uncalcified basis substance or matrix. 




Fig. 35. — Vertical section through coronal region of a tooth, shewing the 
amelo-dentinal junction. Prepared by grinding. Unstained. Magnified 250 
times. E. Enamel; d. Dentine; s. Granular enamel rods of irregular formation. 

Walkhoff summarises his investigations by asserting that 
the club-like processes represent simple dentinal tubes, which, 
through unusual vitality, have opposed sufficient resistance to 
the absorption of the dentine, which takes place during the 
formation of the enamel; and that there were certain masses 
of basal substance already formed round each tube which the 
resorption was unable to destroy. 

The amelo-dentinal line, junction, or boundary, is made up of 
a fairly straight or slightly undulating line with pale homo- 
geneous tissue on either side. The tubules do not end on the 
line, but near it, while the enamel rods themselves are struc- 



48 THE DENTAL TISSUES 

tureless or faintly granular. This condition obtains in hori- 
zontal sections of premolar and molar teeth taken at the 
cervical margin, and at the narrow part of that margin. In 
its broadest part the boundary is represented by a linear 
series of tiny enamel convexities looking towards the dentine. 
Here the tubules are strong and thick and come quite up to 
the edge of the convexities, and the structure of the enamel 
convex surface is pale, bright, and glistening when viewed by 
transmitted light (Fig. 35). The enamel in the immediate 
neighbourhood is translucent and structureless. 1 

The same appearance is found in vertical sections, but the 
enamel crescents are more constant. They closely resemble 
that edge of the layer of formed but uncalcified dentine — the 
dentogenetic zone — in developing teeth which is in juxta- 
position to the calcified dentine. 

As has been already stated, tubules from the dentine with 
or without their bulbous enlargements occasionally cross 
this border. 

1 It is of great interest to note that when sections of sound teeth have been sub- 
jected to impregnation with coloured collodion, as first advocated by Charters 
White, isolated patches of the enamel of this region may become stained. (See 
Fig. 35.) This often occurs, and may show that the chemical properties of the 
enamel are different here. The fact may probably throw some light on the 
actual method of production of secondary enamel decay; and may be regarded 
as an evidence of degeneracy of human enamel. 



CHAPTER IV 

ORTHO-DENTINE 

Microscopical Elements. — (i) Matrix; (ii) Tubes; (iii) Sheaths of 
Neumann; (iv) Interglobular spaces; (v) Granular layer; (vi) 
Schreger'sLines; (vii) Contour lines of Owen; (viii) Laminae. Second- 
ary dentine. 

GENERAL CHARACTERISTICS 

Definition. — That hard tissue 1 of the tooth, which, while 
comprising its greatest bulk, forms the natural boundary of 
its pulp. 

Varieties. — There are four varieties: — Ortho-dentine — hard 
or unvascular plici-dentine, vaso-dentine, and osteo-dentine. 
This is Tomes' classification. Dr. Med. C. Rose, 2 of Leipzig, 
basing his opinion on the definition of dentine as "a hard tissue 
with a smooth surface, which is developed under an epithelial 
sheath (enamel organ), and grows on one side only," groups 
the different kinds under the headings of (i) "Normal tubular 
dentine," (ii) " Vitro-dentine" which contains no protoplasmic 
processes, (iii) "the Vaso-dentine of Tomes," and (iv) "Tra- 
becular dentine." The latter — a new term — is defined as "a 
hard tissue, rich in short dentinal canals, and capable of in- 
crease in all directions; but not growing immediately beneath, 
and in dependence upon an epithelial sheath." Here will be 
considered the first-named variety, viz., hard dentine, or, more 
correctly, ortho-dentine. 3 

1 According to Gallippe (Comp. Rend, des Seances el Memoires de la Societe de 
Biologie, 1884) the chemical constituents of dentine are as follow: Phosphoric 
acid, 23.70 per cent.; Calcium, 45.11 per cent.; Magnesium, 1.67 per cent.; 
Magnesium Carbonate, 1. 13 per cent.; Calcium Carbonate, 0.35 percent.; Silicates, 
0.41 per cent.; Alkaline chlorides and phosphates, 0.54 per cent.; water and 
organic matter (probably collagen), 25.29 per cent.; and an unknown salt, 1.8 
per cent. 

2 "On the various alterations of the Hard Tissues in the lower vertebrate 
animals." From the Analomischer Anzieger, 1898. (Bd. xiv., Nos. 1, 2, and 3.) 

3 In the following pages the use of the word "dentine" is applied to the 
commoner variety, viz., ortho-dentine, — unless otherwise indicated. J 

49 



50 THE DENTAL TISSUES 

Origin. — The matrix or intertubular ground substance is 
formed by calcification proceeding from certain cells of the 
pulp; the walls and contents of the tubules are manufactured 
probably by the columnar cells on the surface of the pulp, 
these as well as the other cells being derived from the stomo- 
daeal mesoderm. 1 

Distribution.— Hard unvascular dentine is found in the 
teeth of man, and most mammals; also in some reptiles and 
fishes. In the adult human dentition it measures about 2 mm. 
in the radicular, and 4 mm. to 5 mm. in the coronal regions, over 
the cornua of the pulp. 

Macroscopical Appearances. — Yellowish-white in colour, dull, 
and slightly lustrous on cleavage. 

HISTOLOGY 

In considering the minute anatomy of dentine, it will be 
convenient to describe its (i) Matrix, (ii) tubes, (Hi) sheaths 
of Neumann, (iv) interglobular spaces, (v) granular layer, 
(vi) lines of Schreger, (vii) contour lines of Owen, and (viii) 
lamellae or laminae. 

(i) The Matrix 

The matrix, or inter-tubular substance, called also the 
basis-substance by some authors, appears to be perfectly 
homogeneous, translucent and hyaline. The researches of 
von Ebner 2 (who first successfully demonstrated the existence 
of a connective tissue stroma in bone) and Howard Mummery 
{Philosoph. Trans. Roy. Soc., 1892), have, however, proved that 
a delicate network of fine connective tissue fibres pervades it. 
The latter says (p. 537) "We can no longer look upon the 

1 Throughout these pages the conventional use of the word "odontoblast" 
(meaning each of the large columnar cells on the surface of the pulp) will be 
retained. The author's view as to the term being a misnomer when applied to 
these cells is well-known; the reader is, however, referred to a Note in the 
Appendix for the arguments. It may be possible, a few years hence, to properly 
attach the name to the other round central pulp cells, and not to the constituents 
of the membrana eboris, which may be designated "pulp corpuscles." 

2 " Histologic der Zahne mit Einschluss der Histogenese," in Scheff's "Hand- 
buch der Zahnhcilkunde," Vienna, 1801. 



THE DENTINE 



51 



matrix of dentine as being a homogeneous substance, but must 
regard it as composed of a reticulum of fine fibres of connect- 
ive tissue, modified by calcification, and when that process 
is complete, entirely hidden by the densely deposited lime 
salts." 




Fig. 36. — Longitudinal section at apex of radicular portion of pulp in Human 
premolar, shewing odontogenic fibres in continuity with the dentogenetic zone. 
Magnified 350 times. {After a drawing by Howard Mummery in the Philosoph. 
Trans. Royal Society.) 

Fig. 37. — Transverse section of pulp of crown of a Human premolar, shewing 
fine fibres in connection with the dentine on one side, and the pulp on the other, 
crowded with cell nuclei. Magnified 230 times. (After a drawing by Howard 
Mummery from the same source.) 




Fig. 38. — Same as preceding drawing, and from the same source. The larger 
nuclei belong apparently to odontoblasts. Magnified 230 times. 

"These fibres decussate freely with one another, and I 
believe them to be analogous to the decussating fibres of bone. 
They are rendered visible, in some instances, by the slow 
decalcifying action of caries, as they appear to resist the 



52 



THE DENTAL TISSUES 



action of acids more than do the lime salts." He suggests for 
these the term "odontogenic fibres." They are, therefore, 







Fig. 39. — Odontogenic fibres. {Photomicrograph by Howard Mummery. 

iSfo 




Fig. 40. — Same as preceding figure. {Photomicrograph by Howard Mummery.) 

most likely, morphologically and chemically, identical with 
those found in the matrix of the bone, and have their origin in 



THE DENTINE 53 

connection with or are closely attached to certain connective 
tissue fibres of the pulp. They are uncalcified. 

(ii) The Tubes or Tubules 

The microscopical examination of a section of dentine, 
whether lengthwise, crosswise, or oblique, whether decalcified 
or not, discloses the fact that, interpenetrating it everywhere, 
are very numerous, fine, ramulous, fastigiated fibril-transmitting 
channels. Ground sections exhibit the tubes better than those 




Fig. 41. — Odontogenic fibres in a vertical section of carious dentine, the de- 
calcification of which has rendered them very apparent. The crown of a molar 
tooth of man. Decalcified by the author's process. Stained with Ehrlich's 
acid haematoxylene. Magnified 420 times. D. Dentine; p. Pulp; o.f. Odonto- 
genic fibres. 

chemically softened, because they retain debris and air, and 
are thus more strikingly differentiated from the matrix. 

When viewed vertically, it is at once apparent that the 
tubes run centrifugally and radially from the pulp-cavity. 
They maintain a certain amount of coincidence with the 
direction of the peripheral cells of the pulp (the so-called 
odontoblasts) — that is, they leave the soft tissue in lines 
nearly always continuous with the long axes of the odontoblasts. 



54 



THE DENTAL TISSUES 




Fig. 42. — Vertical section of dentine, coronal portion, showing'the arrange- 
ment of the primary curvatures of the tubules. Unstained. Magnified_40 
times, e. Enamel; d. Dentine; f. Interglobular spaces. 



THE DENTINE 



55 




Fig. 43. — Vertical section, of dentine, radicular portion, showing the branch- 
ing and terminations of the tubules. Prepared by grinding, after staining by 
impregnation with 'coloured collodion. Magnified 240 times, d. Dentine; 
C. Cementum. 



56 



THE DENTAL TISSUES 




Fig 44. — Transverse section of dentine, radicular portion, shiwing the radia- 
tion of the tubes from the pulp cavity. Prepared by grinding. Unstained. 
Magnified 40 times. D. Dentine; c. Cementum. 



THE DENTINE 



57 



They are arranged side by side in an approximately parallel 
manner to each other. 

In width they vary from 1.7^ to 2.2/z, or 5m (Kolliker); 
2. 5m (Owen); 1 or 0.0055 mm - — an average measurement — at 
their pulpar or large extremity (Schafer in "Quain's Anatomy," 
Vol. II., Part I., 191 2). The distance between their mouths 
may be considered to be twice or thrice their diameter in the 
same situation, where, too, it — the distance — is fairly regularly 




Fig. 45. — Longitudinal section of dentine. Prepared by grinding. 
Magnified 420 times. 



maintained. No hard-and-fast statement can, however, be 
made on this point, as the amount of intervening matrix is 
greater or less in different parts of the tooth and of the teeth 
in the same mouth. The diameter of the tubes diminishes as 
it proceeds outwards, till at the cervical region of the tooth it 
becomes immeasurable. Their greatest lengths may equal from 
5 mm. to 6 mm. 

The inner extremity of a canal is a wide open orifice looking 
on to the surface of the pulp; the other near the enamel or 

1 "Odontography," p. 459, 1840. 



58 



THE DENTAL TISSUES 




Fig. 46. — Dentine Nearly transverse section. Prepared by grinding. 
Stained bv Weil's process. Magnified 160 times. 




Fig. 47. — Dentine. Oblique section, showing the branches of the tubes. Pre- 
pared as in last figure. Magnified 420 times. 



THE DENTINE 



5<> 



cementum is a cul-de-sac of large dimensions in the former 
locality, and generally one or more minute spherical knobs 
in the latter. Those in the coronal part of the tooth run 
vertically from the pulp cavity, at the cervical margin obliquely, 
and in the radicular region horizontally or with an inclination 
towards the apex. This difference in direction is gradually 
brought about, and varies considerably in different specimens 
(Fig. 42). 




Fig. 48. — Dentine, radicular portion, showing secondary curvatures of the tubes. 
Magnified 160 times. {Photomicrograph by Douglas Cabell.) 



Each tube describes in its somewhat divergent course certain 
curves or flexures. These are called the "primary" and 
"secondary" curvatures of the dentinal tubules. The former 
are more marked in the crown than the root, the latter the 
root than the crown; the former are large, gentle undulations, 
the latter small spiral twists; the former are on the same plane 
or nearly so, the latter not on the same plane; the former two 
or three in number, the latter very numerous, as many as two 
hundred in a line — K2 of an inch — according to Retzius. 



60 THE DENTAL TISSUES 

Welcker has likened a tubule to "the thread of a corkscrew 
stretched so that the turns are drawn far apart," its breadth 
thereby being proportionately diminished. In thick longitu- 
dinal and transverse sections of the dentine of the root this 
corkscrew-like appearance is easily noted (Fig. 48). 

The tubules of dentine in deciduous teeth are sometimes 
constricted at short intervals, and thus present a moniliform 
appearance. 




r . 



Fig. 49. — Dentine. Coronal portion, showing tubes and spherical dilatations 
of the termination of the branches. Prepared by grinding. Unstained. Magni- 
fied 160 times, d. Dentine; e. Enamel; a. Amelo-dentinal junction. 

Further, at the cervical regions of the deciduous teeth the 
tubes make a conspicuous, sudden, extensive bend in their 
courses, in addition to the primary and secondary curvatures 
just noted. These curves are in a direction downwards and 
outwards toward the gingival edge. The result is the formation 
of that peculiar prominence or ridge of enamel, itself not in- 
creased in amount, at the cervical portions, which is so 
characteristically displayed in the teeth, (particularly the 
molars,) of the deciduous series, thus producing the appear- 
ance of great constriction at their necks. This does not occur 
in the permanent dentition. 



THE DENTINE 



61 



Branches. — As they proceed outwards, the tubes give off 
exceedingly fine subsidiary tubes. These are branches which 
somewhat simulate those on a twig of a tree. They come off 
alternately and laterally from the stem or main trunk, some- 
times at right, sometimes at acute angles to it; they are par- 
ticularly abundant in the dentine of the roots, less frequent 
in or almost absent from that of the crowns, where they are 
chiefly found as the tube approaches its free termination. These 




Fig. so. — Dentine, radicular portion, showing branches of the tubes, d. 
Dentine; c. Cementum. Prepared and photographed by Dr. H. Box, Royal 
College of Dental Surgeons, Toronto. 

channels may end, either in the form of branches or not, (i) 
in tiny spherical culs-de-sac near the margin of the enamel; 
(ii) by anastomoses with their neighbours — ''the terminal 
loops" of Kolliker; (hi) ,, in .the -interglobulai spaces; (iv) 
in the granular layer of Tom.&s:; (v) ,i.-i the cementum;- «(vi) in 
the enamel-spindles beyond the amejod^tiaah/urtc'.ionpr (vii) 
as straight caecal terminations in the. intercolamnar cement 
substance. In the crown they often divide t'ichotomously 
(i.e., by pairs). These divisions, most commonly observed 
near the pulp cavity, are frequently bifurcations which Kolliker 
has described as being "repeated two to five times or more, 



62 



THE DENTAL TISSUES 



so that at length four, eight, sixteen or more canals may arise 
from a single one." He also mentions certain "ramifications" 
which would seem to him to be the sub-divisions of the main 
tubes. He says {op. cit. p. 291) "the canals, now narrower 
after their division, run close together and nearly parallel 
towards the surface of the dentine; and, except in the root, 
just begin to send out ramifications in the outer half or outer 
third of their course. These ramifications appear in the roots, 




V*NV V 



Fig. 51. — Terminations of the dentinal tubes in the spaces of the granular 
layer of Tomes. Prepared by grinding. Unstained. Magnified 420 times. 



chiefly as fine branches issuing from the main tubes, but in the 
crown bifurcated terminations of them. In the latter case 
they, are. for the most part few in number: it is otherw'se in the 
iQO,tj where .the branches, ;b»ing .generally close to each other, 
and passing off from the j canals at right or acute angles, give 
them sometirties the appearance of a feather, sometimes of a 
brush, the la^er especially when the branches are large and 
ramify still more,.". 

The off-shoots, like the main tubes, taper towards their 
terminations. 



THE DENTINE 



63 



Transverse sections of dentine, in which the tubes are cut 
across, show abundant rounded piercings of the matrix, each 
having a slightly modified boundary or wall. The boundary 
is represented by a yellowish ring — black or grey if stained 
by Golgi's rapid process — which, when unstained, is often 
quite unrecognisable; but nevertheless exists as one of the 
sheaths of Neumann. The walls are very minute, and, in 
thickness less than the diameter of the aperture of the tubule. 




Fig. 52. — Dentinal tubes 



transverse section. Prepared by Weil's process. 
Magnified 800 times. 



Kolliker gives a description of and pictures {op. cit. p. 291), 
a transverse section through the dentine of the roots of teeth 
in which the tubes are intimately connected by extremely 
numerous anastomoses. Probably it was taken close to the 
pulp surface, as there are no indications in the drawing of any 
spherical or other termination of the branches. 

The channel, in the fresh state, contains the dentinal fibril 
and lymph. The former in transverse sections appears like a 



64 



THE DENTAL TISSUES 



delicate roundish dot. 1 This does not necessarily occupy the 
centre of the canal, although it is most probable that during 
life it fills, or very nearly fills, its entire length. It is impossible 
to prepare, for histological purposes, sections of the hard and 
soft tissues of teeth in combination, without altering their 
normal characteristics. Hence it seems reasonable to believe 
that not only does the protoplasmic filament traverse the tube 
from pulp to extremity, but that also it rarely, if ever, com- 
pletely occludes it. 

It is evident that the contents of the tubules are proto- 
plasmic processes or fibrils which emanate from the odonto- 
blasts of the pulp. They represent their distal or dentinal 



10 10 



■U 



old 



Fig. 53. Fig. 54. 

Fig. 53. — Diagram shewing Tomes' conception of relations of (o) Odontoblasts; 

(f) Dentinal fibril; (t) Dentinal tube, with its sheath; and (m) Matrix. 

Fig. 54. — Klein's conception of the same. 



processes. E. Klein, "Atlas of Histology," 1880, p. 185, 
considers that the odontoblasts do not furnish the dentinal 
fibrils. He says: "I cannot find convincing evidence of the 
odontoblasts doing more than producing the dentine matrix. 
The dentinal fibres appear to me to be derived solely from the 
deeper layer of cells which are wedged in between the former." 
The fibrils themselves are soft structureless threads, devoid 
of a covering of any kind, and continuous through all the length 
of the tubule and its branches. They are bathed during life 
with a serous exudation from the surface of the pulp. This 

1 Bodecker, "Dentin, Cement und Schmelz," in Heitzmann's "Mikroscopische 
Morphologie," Vienna, 1883, describes the fibrils as angular, not round — under 
enormous magnifications. He thinks they give off tiny off-shoots which run 
into the matrix of the dentine through the sheaths of. Neumann. The action 
of reagents used for fixing and hardening the fibrils in situ produced this effect 
of angularity. The processes of cells in other parts of the body are never angular 
in cross-section. 



THE DENTINE 65 

exercises, no doubt, a trophic influence upon them, and prevents 
injury, which might occur if they were brought into immediate 
contact with the lining membrane of the tubule. 

All authors are not agreed on this elementary question 
of their contents. Magitot ("Traite de Carie Dentaire," 
1878), says that "during life the dentinal canaliculi contain 
a colourless transparent fluid;" and Morgenstern ("Ueber 
die Innervation des Zahnbeins" in "Archiv. fur Anatomie 
und Physiologie," 1896), declares he has seen many nerve 
filaments in the tubes. "It is the dentinal canaliculi," he 
writes, "which for the most part contain the larger nerve 
filaments." His arguments are weak and valueless, depend- 
ing as they do on the results obtained from the vagaries of 
so uncertain and unreliable a method of staining as that of 
Golgi, when applied to sections of dentine. 

The matrix and tubes of dentine show marked translucency 
in places, especially the roots, in senile and functionless teeth. 

(iii) The Sheaths of Neumann 

After careful decalcification there remains a soft, mucoid, 
felt-like mass, the organic part of dentine — the walls of the 
tubes. Highly elastic and slightly cohesive to the inter- 
mediate matrix, when thus isolated the sheaths look like 
long yellow-elastic connective tissue-fibres: but they are, of 
course, quite hollow. They possess no histological signifi- 
cance. They were first accurately and most fully described 
by Neumann in 1863. 1 He demonstrated that all soft tissues 
of the tooth having first been removed, subsequent macera- 
tion in boiling acids, of various strengths for varying periods 
of time, led to dissolution of the whole of the inorganic elements, 
and left behind a tube-like formation, which was characterised 
by, and distinguished from, the dentine matrix by the peculiar 
property of resisting the action of chemical substances, and by 
great elasticity, and slight cohesion with the inter-tubular 
material. Some attention has lately been again given to the 

1 "Ein Beitrag zur Kenntniss des Xormalen Zahnbein-und Knochen-gewebes." 
Leipzig. 



00 



THE DENTAL TISSUES 



question of the existence or non-existence of these sheaths; and 
interest revived in what seems a simple, but is, in reality, 
a complex study. 1 Optical effects are so easily produced when 
examining dentine: its collagenous substance is so hard: its 
association with the soft protoplasmic easily-destructible soft 
tissues so direct and complete, that it can be no small matter for 
wonder that investigators still hold opposite opinions which 
give rise to considerable confusion. 




Fig. 55. — The sheaths of Neumann. Prepared by decalcification and teasing 
out. Stained with borax-carmine. Magnified 240 times. 



Neumann affirmed that the tubules possess proper walls. 
He called them "Dental Sheaths" ("Zahnschieden") and he 
added that: "In the dental tubes are contained fibrous non- 
calcified processes of the peripheral pulp-cells ("Tooth-fibres"). 
In this way was corroborated the original statement of John 
Tomes in 1856, in his classical contribution to the Philosoph- 
ical Transactions of the Royal Society, entitled "On the presence 
of fibrils of soft-tissue in the dentinal tubes." 

1 "A Study of the Minute Structure of Dentine" by Dr. Kanae Hanazawa, 
Tokyo. "The Dental Cosmos," 191 7. 



THE DENTINE 



6 7 



Kolliker, who actually first discovered them by acid macera- 
tion, points out that the apparent walls of the tubes in trans- 
verse sections are not the real walls, but a certain length of the 
canals themselves, which appear as dark rings. If, however, 
an edge, very narrow in width, and yellowish in colour, is seen, 
this he regards as the true wall (" Mikroscopische Anatomie," 
Leipzig, 1854). 

Oscar Romer denies in toto the existence of these sheaths 
of Neumann. In his monograph already quoted, Part I. is 
devoted entirely to the consideration of their presence or non- 
presence in dentine. According to his measurements, they 
are i/u to 2/x in width at their broadest part. He contends 
that the contents correspond to the walls of the tubes; in other 
words, "that the odontoblast processes (or dentinal fibrils), 



Fig. 56. — Diagram showing Romer's conception of relations of (o) Odontoblasts; 
(f) Dentinal fibril; and (m) Matrix. 



really correspond to Kolliker 's dentinal tubules," are therefore 
hollow, and continue as, and do not enter into Neumann's 
sheaths. He sums up his arguments with the following asser- 
tions : — 

(a) The fibrils described and depicted by Tomes in 1856 
are no new formations, but completely identical with 
the dentinal fibrils described by Kolliker in 1834, while 
Tomes' membrane of the fibrils corresponds to the wall 
of the tubules, and to Neumann's sheath; and the con- 
tents of the fibrils, described by Tomes as semi-fluid, 
correspond to the contents of the tubules described 
as fluid by other writers. 

(b) The dentinal tubes assumed by Tomes do not correspond 
to the dentinal tubules of Kolliker, but are artificially 
produced, wall-less, tube-shaped hollow spaces produced 



68 THE DENTAL TISSUES 

in the matrix of dentine by decalcification and dissolution, 
spaces from which Kolliker's tubules and Tomes' tubes 
can be easily isolated. 
(c) The odontoblast processes, designated "Tooth-fibres" 
or "Tomes's fibres," are not the contents of Kolliker's 
dentinal tubules, but represent both the sheath of Neu- 
mann and the contents together. Therefore, the concep- 
tion of " Tooth fibres " or " Tomes's fibres," as the contents 
of Kolliker's tubules, must be dropped, and we must con- 
tent ourselves for the present with the original assumption, 
that the contents of the dentinal tubules are a fluid or 
semi-fluid material, or one that has not yet been adequately 
investigated. 
And he concludes: — "According to my observations, there do 
not exist in the dentinal substance any tubules other than those 
of Kolliker. The dentinal tubes of Tomes are only tube- 
shaped holes produced in the dentinal substance by maceration; 
one cannot perceive, even under the strongest magnifying 
power, and even in stained section-preparations of normal 
non-carious dentine — whether in transverse, longitudinal, or 
diagonal section — any intervening space whatever, between 
odontoblast process (or the dentinal tubule) and the matrix 
of the dentine." Romer's observations are entirely faulty 
and untrustworthy; for the processes of cells in other parts of 
the body are never hollow — with the possible exception of the 
cilia of ciliated columnar epithelium, which are highly specalised 
processes of the cells endowed with movement. 

The various contradictory theories concerning the existence 
and non-existence, the walling, and the contents of the dentinal 
tubules may be briefly mentioned as follow: 

(i) Their absence is affirmed by Magitot (1880). 
(ii) Their presence in mature dentine is denied by Xavier 
Sudduth (1887), who ("American System of Dentistry," 
p. 594) ,_ says: "The salts of calcium are deposited 
around the fibrils of the odontoblasts, and in a certain 
sense, dentinal tubuli may be said to exist at that time. 
We may say that this tissue is an aggregation of tubes 
containing fibrils, but in the process of aggregation they 



THE DENTINE 69 

lose their identity as such, becoming cemented to- 
gether into a solid tissue." And further, "The fact that 
dentine is not capable of being broken up into tubes is, 
in my mind, conclusive evidence against the theory of 
the existence of a dentinal sheath per se as the wall of a 
dentinal tube." 
. (iii) There are two kinds of tubules in dentine, one con- 
taining the processes of the odontoblasts, the other, 
finer, to receive nerve fibres. An unproved postulate 
of Franz Boll, 1868, " Untersuchungen fiber die Zahn- 
pulpa" in "Archiv ffir Mikroskopische Anatomie." 
Bd. iv. 

(iv) The processes of the odontoblasts (dentinal fibrils) 
are Kolliker's dentinal tubes. Lent, 1885, "Ueber die 
Entwickelung des Zahnbeins und des Schmelzes," 
" Zeitschr. fur wissensch. Zoologie," Leipzig. 

(v) The sheaths of Neumann are dependent on calcified 
dentine substance, because they are invisible (absent) 
in the dento-genetic zone. Erwin Hohl, 1896, "Beitrag 
zur Histologie der Pulpa und des Dentins" in "Archiv 
fur Anatomie." 

(vi) The membrane of the processes of the odontoblasts 
form the sheaths which run in wall-less tubes. The 
sheaths in situ are wider than those artificially isolated 
by acids. Romer, 1899, op. cit. 

(vii) Their existence as separated structures is doubted by 
Underwood, "Aids to Dental Anatomy and Physi- 
ology," 1902. 
(viii) The tubules have definite walls (sheaths), and contain 
Tomes' dentinal fibrils, — processes from certain cells 
of the pulp. Tomes op. cit. 1914; as well as many 
other authors. 

(iv) The Interglobular Spaces of Czermak 

At varying distances below the amelo-dentinal junction are 
found in apparently sound as well as in imperfectly developed 
dentine numerous globular markings arranged in linear series, 
and running transversely to the dentinal tubes. Defective 



7° 



THE DENTAL TISSUES 



dentine exhibits them remarkably well. They were first 
described by J. Czermak in 1850, and designated by him the 
"interglobular spaces." "Beitrag zur Mikro-Anatomie der 
Menschlicher Zahne." 

As Tomes has pointed out, they are due to an arrested 
development of the tissue during certa n early stages of its 
growth, when, for some cause or other, the calco-globular 




Fig. 57. — Interglobular spaces crossed by dentinal tubes. Prepared by Weil's 
process. Magnified 240 times. 

masses have not fused, or have only partially melted together. 
The functions of the lime-bearing cells of the pulp have become 
temporarily modified, and instead of the dentinal basis-sub- 
stance being deposited in proper amount and regularity — 
making a homogeneous whole — the calco-globular masses have 
remained unchanged or slightly changed, and the matrix has 
flowed around, and become, in time, fully calcified. 

Seen under advantageous circumstances, e.g., in sections 
which have been carefully ground thin, and stained by Golgi's 
silver chroma te method, or impregnated with coloured collo- 
dion, the spaces vary greatly in shape and size. Their scalloped 
edges are made up of the rounded or oval margins of spheres 



THE DENTINE 7 1 

of calco-globulin mutually pressed together. If these bodies 
retain their rotundity, the spaces have here three, four,- five, or 
more concavities forming their outline, the semi-lunes being 
often dissimilar in size and shape; there, they have a lobulated 
appearance; while elsewhere, by the process of union of two or 
three spaces, they become elongated and irregular. In dia- 
meter they vary from 2.5/i. to 4.2,11, or less. 

As to their contents they are generally believed to hold 
in their interiors, in the fresh state, soft protoplasm which 
fills them entirely. Dentinal tubules often traverse them. 
Tomes has proved this by noting in fragments of carious den- 
tine, that the tubules which cross, not only contain micro- 
organisms, but have themselves become occasionally enlarged. 
The protoplasm, under favourable conditions, undergoes cal- 
cification, and the dentine is said to be areolated. 1 

Dentinal tubules may terminate in the interglobular spaces. 

In dried sections, they contain air, a fact which is easily 
demonstrated by soaking thin slices of dentine in coloured 
collodion, which runs into and fills every part. They are 
therefore in dried specimens veritably "spaces." 

(v) The Granular Layer of Tomes 

In the radicular portions of teeth, and beginning at the 
cervical margin, is the granular layer. It stretches as a fairly 
thick black or grey band, round the roots, at the periphery of 
the dentine immediately internal to the cementum. It pre- 
sents the appearance, under low powers, of a line of black 
grains of sand. Near the neck of the tooth the layer is narrow, 
but as it reaches the apical foramen, it broadens out con- 
siderably, and soon is more pronounced. This is not, however, 
constant. The author possesses a section in which the rows of 
interglobular spaces and the granular layer are coalescent at 
a spot immediately subjacent to the ending of the enamel 

1 These areolations of dentine are most likely perfectly analogous with those 
irregularly shaped layers made up of solid rounded calcined bodies seen occasion- 
ally near the surface of the shafts of long bones, lying in their osseous laminae. 
They differ, however, in the fact that, whereas the former betray certain develop- 
mental defects, the latter mark various sites of absorption and re-deposition of 
bone. 



r~ 



THE DENTAL TISSUES 



at the cervical region; and here the latter is very broad and 
marked. In some sections it is hardly at all visible. 

On closer examination, these multitudinous dots assume 
various irregular shapes. Some are more or less circular, 
others oval; some triangular, others quadrate; some clavi- 
form, others stellate; a granule — in a word — represents a 
compromise between an interglobular space and a lacuna in 
hyperplasic cementum. 




Fig. 58. — The granular layer of Tomes. Prepared by grinding and staining 
with coloured collodion. Magnified 240 times, d. Dentine; c. Cementum; 
G. Granular layer. 

Many instances are noted where the terminations of the 
dentinal tubules end in these tiny spaces; and when canaliculi 
seem to led from them, they can be traced to one of the endings 
of a tubule. 

Approaching the apex of the root, the spaces increase greatly 
in numbers, and are much larger and more irregular. Occa- 
sionally, a large spindle-shaped lacuna may be found. The 
layer is situated in a matrix of dentine which is distinctly 
granular; though the term "granular layer" refers obviously 
to the spaces. 



THE DENTINE 



73 



Their contents, according to Bodecker, are soft protoplasm 
which is in connection with the contents of the tubules on one 
side, and the canaliculi of the cemental lacunae (when they 
exist) on the other. It would seem, however, that it is by no 
means easy to prove this assertion. The granular layer is 
stained with the utmost difficulty by the action of carmine or 
any of the other basic, acid, or aniline dyes. It is more likely 
to be beyond the pale of nutrition. 

Bounding the granular layer externally is a very narrow 
strip of homogeneous dentine: then comes a dark line — it is 
nothing more than that — which forms the point of demarca- 
tion between dentine and cementum. The homogeneous zone 
and this line are devoid of any structure whatever. 




Fig. 59. — Schreger's lines in dentine. From the ivory of the tusk of a walrus. 
Prepared by grinding. Unstained. Magnified 45 times. Cf. Fig. 26. 



(vi) Schreger's Lines 

These, sometimes seen in horizontal sections of dentine, 
must not be confounded with Schreger's lines in enamel. 
Many of the dentinal tubes as they course outwards form the 
artificial appearance of bands, through the primary curvatures 
passing in the same direction. Thus, Schreger's lines are 



74 THE DENTAL TISSUES 

merely markings which, running parallel to the external edge 
of dentine, are produced by the coincidence of the primary 
curvatures of the tubules (see Fig. 60). 

They are well — perhaps best — exhibited in sections of the 
ivory of the tusk of the walrus, where they appear to be due 
to sudden short bends or twists of the primary curvatures, oc- 
curring at identical places in their lengths. The effect under 
low powers is a much striated character of the tissue. 




Fig. 60. — Same as the preceding. Magnified 420 times. Cj. Fig. 27. 

(vii) The Contour Lines of Owen 1 

comprise (i) Schreger's lines in dentine, and also (ii) rows of 
so-called "dentinal cells." Under low powers these rows 
resemble lines, particularly in human molars and in the teeth 
of Cetacea, and it is to them that he refers when he describes 
them as "contour lines." On page 460, he says, "Both the 
primary and secondary curves of adjacent tubes are parallel; 
and occasionally the tubes make a short bend along a line 
parallel with the outer contour of the crown, giving rise to 
the appearance which may be called "contour lines," the par- 

1 Owen: "Odontography," 1840. 



THE DENTINE 



75 



allelism of the entire tubes being affected only by the amount 
of divergence in radiating from the pulp cavity." Again 
(p. 464), "These lines are not equally conspicuous in every 
tooth; I have usually found them most so in the molars of 
the human subject, where without being regularly equidis- 
tant, they have presented intervals of about one hundredth of 




Fig. 61. — Contour lines of Owen in dentine. Vertical section of Human 
molar. Decalcified. Stained with Ehrlich's acid haematoxylene. Magnified 
40 times. L. Owen's lines, running in a transverse direction. 

an inch, commencing at thrice that distance from the periphery 
of the dentine." 

With regard to the last-named histological formation, i.e., 
the "dentinal cells," Owen remarks, "In many teeth, more- 
over, and especially in the tusks of the elephant, the secondary 
branches of the dentinal tubes dilate into intertubular cells 
along lines, which in like manner are parallel to the coronal 



76 THE DENTAL TISSUES 

contour of the tooth; hence another cause of the appearance 
of concentric lamellae, and of the actual decomposition of 
such teeth into super-imposed lamelliform cones." These 
dentinal or " calcigerous cells," as this distinguished author 
also designates them, form many layers having a certain 
amount of parallelism with the contour of the pulp cavity. 
He described them first in a Report to the British Asso- 
ciation in 1838 (vol. vii., p. 144). They are not animal 
cells in the modern acceptance of the term, but in the inter- 
spaces of the tubes they include a "tubular structure." "The 
intertubular space is not cellular, but clear and structureless." 
To-day, histologists would prefer to think of them as repre- 
senting merely the calcified outlines of what might have been 
interglobular spaces. Owen's contour lines were seen by 
Salter, 1 who, however, prefers to call them "incremental lines," 
as indicating more accurately the manner in which the tooth 
substance is built up. 

(viii) Lamella or Lamince 

Occasionally, though seldom, vertical sections of roots or 
human molars, when ground, reveal very clearly certain 
markings in the periphery of the dentine. Ranged at right 
angles to the tubules, and running concentrically with the 
pulp chamber, these short straight strips are very numerous 
in some sections, sharply defined and bright when unstained, 
of variable length, and cross the tubes near their extremities. 
They are non-pathological in origin, and are not artificially 
made by the action of reagents. Most probably they re- 
present marks of stratification during the development of the 
tissue. 

A second class of laminse is often seen in the matrix of 
mature dentine when decalcified in hydrochloric acid, and 
stained with haematoxylene. Vertical-transverse (labio- 
lingual) sections of molars, show over the cornua of the pulp, 
regularly arranged faint shadings, separated by brighter 
less-coloured lines; and in the cervical and radicular regions, 
rounded dots (which are probably the same as Owen's dentinal 

1 "Dental Pathology and Surgery," page 10, 1874. 



THE DENTINE 77 

cells 1 ) of darker colour near the pulp, and near the cementum 
long looped lines running in the direction of the tubes. These 
long lines or laminae are joined at their distal ends by delicate 
arcuate markings, the concavities of which always look to- 
wards the pulp. 

Thus, lamellae in dentine include two groups: the former, 
short, tube-like, straight; the latter, long wavy bands and 
spherical shadows, and lines joined by an arch. 

These laminae are not due to staining, nor are they optical 
illusions. The first group obtains in natural conditions; while 
the others are evidently rendered more apparent by decalcifica- 
tion, and more striking by staining. They both certainly 
indicate the manner in which calcific deposition has taken 
place. 

F. J. Bennett, 2 in a paper on "Certain points connected with 
the Structure of Dentine;" has described laminae in dentine 
which has been acted upon, for some length of time, by glyc- 
erine. In certain longitudinal sections the dentine bordering 
the margin of the pulp cavity "presented a ringed appearance, 
and was slightly laminated." This was due to "the dentinal 
tubes, in this situation, having lost their surrounding inter- 
tubular tissue, which left them clearly defined; but this removal 
of the matrix had not completely freed them. Their course 
appeared to be interrupted, at regular intervals, by layers of 
membrane having a general direction parallel to the surface 
of the pulp. The layers of membrane (laminae) bore a general 
resemblance to that seen in interglobular dentine; in this case, 
however, circular apertures and not solid globules occupied 
the surface of the membrane. Oval spaces were also found 
between the layers of membrane." Bennett put forward the 
following hypotheses, as being the explanation of such 
phenomena: 

(a) The laminae might represent a part of the matrix of 
dentine, which, possessing a greater power of resisting the 
solvent action of glycerine than the rest, represents a new 
transitional stage or phase in its calcification; or 

1 Owen's "Odontography." PL xcv. fig. 2, also cxiii., fig. 2, and cxix., fig. 1. 
2 Trans. Odonto. Soc. of Gt. Britain, Vol. xxi., p. 6, 1889. 



78 THE DENTAL TISSUES 

(b) Unequal expansion or contraction of certain parts of 
the matrix, producing separation of the layers; or 

(c) Evidences of cell structure in the matrix. 

SECONDARY DENTINE 

Secondary dentine is a physiological product. In the 
strictest sense of the term, it should be used to designate 
every form of new tissue deposited in the substance or on 
the surface of the pulp, which occurs after full development 
of that organ and of the dentine. It has been hitherto used, 
however, for describing both physiological and pathological 
conditions. Salter's 1 patient and remarkable investigations 
in that particular portion of dental pathology which deals 
with degenerative changes in the dental pulp, led him to 
classify all forms of dentinal deposition as secondary dentine, 
and in a sense this was perfectly correct. But the term seems 
to require a more definite meaning; for he describes under 
this one heading three kinds: — "Dentine of repair," "dentine 
excrescence," and "osteo-dentine" or "intrinsic calcification." 

It would be more correct in modern days, since so many 
varieties of pathological dentine have become known, to 
restrict the expression entirely to physiologically constructed 
dentine found, e.g. (i) in the incisive margins of the persistently 
growing teeth of Rodentia, etc., in Man (ii) in the accompani- 
ments of old age, or (iii) the deposits sometimes found in long- 
retained deciduous teeth. Senile teeth constantly possess a 
complete mass of secondary dentine occluding the pulp cavity, 
the occurrence of this having been brought about in a physio- 
logical manner. As a non-pathological result of an active state 
of the pulp, secondary dentine may lastly be associated with 
(iv) attrition, abrasion or fracture of the teeth, when not 
complicated by caries of enamel or dentine. 

1 "Dental Pathology and Surgery,'* chaps, xi. and xii., 1874. 



CHAPTER V 

THE CEMENTUM 

Microscopical Elements: (i) Matrix; (ii) Incremental lines; (iii) 
Perforating fibres. 

GENERAL CHARACTERISTICS 

Definition.- — The thin hard substance 1 situated immediately 
external to the dentine of the roots of teeth of Man and many 
animals. 

Origin.- — It is a product ot the osteoblasts of the perio- 
dontal (alveolo-dental) membrane, i.e., the thin inner layer of 
the dental capsule. 

Distribution. — In the great class Mammalia cementum or 
crusta petrosa — a former appellation — forms the cortex of the 
radicular dentine: but also in the ox, horse, elephant, capy- 
bara, and other animals, it not only unites the roots of teeth, 
but before attrition has taken place, exists as the coronal 
integument. 

In Man, it normally measures, in width, from 175M to 250^. 

It is rarely found in the teeth of Pisces and Reptilia; and is 
normally absent from the roots of anchylosed teeth. Ovarian 
teeth also do not always possess it. 

Macroscopical Appearances. — Whitish - yellow in colour, 
smooth, dull, line of junction with enamel pronounced and 
darker than rest of cementum. 

HISTOLOGY 

The structures calling for special microscopical attention in 
this the least important of all the hard dental tissues of man, 
are, (i) Matrix, or basis-substances; (ii) Incremental 'lines; 
and (iii) Perforating canals and fibres. 

1 The chemical composition of human cementum is unknown. 
79 



cSo 



THE DENTAL TISSUES 

(i) The Matrix 



The matrix or basis-substance makes up the greater part 
of the tissue. It extends as a narrow non-vascular lamina 
round^the roots of teeth external to the homogeneous layer of 
dentine, beginning at the cervical region and covering over 
the apices of the roots, though like the dentine it is discon- 
tinuous at" the apical foramina. Its relationship to enamel has 
already been alluded to; its relationship to dentine is such as 




FlG. 62. — Granular appearance of cement 
{Photomicrograph by Ni 



matrix. Magnified 1,000 times. 
m Broomell.) 



to make it difficult, if not at times impossible, to determine 
where the one begins and the other ends. Often no sharp 
line of demarcation — as in the case of enamel and dentine — 
exists. 

The general appearance of this tissue varies very much — 
thus it may be hyaline, finely granular, or even made up of 
bodies of an amorphous type. 

It is capable at times of being stained, especially at its outer- 
most part. Normal cemental matrix in young and old sub- 
jects is therefore nearly structureless. Roots of simple teeth 



THE CEMENTUM 8 1 

unaffected by morbid processes show this thin layer, which 
maintains the same degree of thinness throughout its whole 
extent. In the case of bi-rooted premolars or molars, how- 
ever, there is a tendency for it to become slightly thicker on 
their alveolar or inner aspects. In old age it is somewhat 
thicker (see Chapter III, Vol. II). 

But in every section of cementum, faint shadings of a slightly 
different refractive index to other parts of the tissue can, on 




Fig. 63. — Same as preceding. Magnified 420 times, d. Dentine; c. Cementum. 

careful examination, be clearly differentiated. Normally they 
are but feebly revealed. These shadings are arranged in two 
ways: The more pronounced run parallel to the periphery, and 
without doubt represent immature incremental lines: the others, 
which are very numerous, cross the first-named at right angles. 
Both classes can be observed in vertical as well as horizontal 
preparations (Fig. 66). 

In thus describing the minute organisation of this tissue, 
the author would like to emphasize the fact, that in his opinion, 
formed as the result of the examination of many sections, 
the cementum of the teeth of. man is usuallv free from lacuna? 



THE DENTAL TISSUES 




Fig. 64. — Incremental lines. Prepared by grinding. Unstained. Magnified 
400 times. 




Fig. 65. — Perforating canals and fibres in cementum. Prepared by grinding. 
Stained with chloride of gold. Magnified 40 times, c. Cementum; h. The 
homogeneous layer of dentine; d. Dentine. 



THE CEMENTUM 



83 




Fig. 66. — Cementum. Prepared as in last figure. Incremental lines and 
homogeneous layer well defined. Magnified 400 times. L. Incremental lines; 
H. Homogeneous layer. 




Fig. 67. — Longitudinal lamella? of cementum, showing numerous varicosities. 
Magnified 1,000 times. (Photomicrograph by Norman Broomell) 



g4 



THE DENTAL TISSUES 



and canaliculi, being nothing more nor less than a dense, solid, 
nearly homogeneous band of calcified basis-substance, ex- 
tending round the roots. The teeth of monkeys and sheep 
(root portions) have been inspected microscopically; and 
here, as in man, it exists as a thin strip almost devoid of his- 
tological elements, such as those characteristic of bone. In 
the opossum and certain other marsupials, however, a thick 
layer of cementum is found sufficiently often to be practically a 




Fig. 68. — Striated cementum from radicular region of tooth, near apex, to 
show the complex character of the thicker tissue, viz.: "The longitudinal striae, 
transverse fibres, cement-corpuscles and zones of apparently unbroken granular 
matrix." Magnified ioo times. {Photomicrograph by Norman Broomell.) 



characteristic of this class. The reader is referred to page no 
in this connection. This lack of lacunas in normal cementum 
has also been observed by Otto Walkhoff (op. cit. pp. 142, 143) 
and figured by him in Plates v. and ix. : both statement and 
photographs having been brought to the notice of the writer 
since the preceding lines were penned. 

But one of the after-effects of a morbid change or a series 
of morbid changes in the alveolo-dental periosteum- — however 



THE CEMENTUM 85 

slight, is the stimulation of the otherwise quiescent osteo- 
blasts, to deposit osseous material on the periphery of the tissue: 
and lacunas are then formed, imprisoning the osteogenetic 
cells. A single lacuna may not infrequently be observed 
situated near the granular layer of Tomes; and this would 




Fig. 69. — To show partial calcification of the incremental lines. Magnified 
1,000 times. {Photomicrograph by Norman Broomell.) 

indicate abnormal processes going on about the time the 
earliest deposited cementum is completed. There is, there- 
fore, under healthy conditions, no chain of living matter 
joining the pulp to the periodontal membrane. 

(ii) Incremental Lines 
represent the marks of stratification during development. 
They look like sinuous unbroken lines placed in a fairly regular 



86 THE DENTAL TISSUES 

and uniform manner one over the other. Sharply marked 
off from the rest of the matrix, at times, and running in a 
parallel direction to the long axis of the root, they give rise to 
a lamellated structure (Fig. 67). 

In young cementum the lamellae correspond in number over 
all portions of the root, the only difference being that they are 




Fig. 70. — Transverse section of an adult premolar near apex, to show the 
varying disposition of the lamellas. The incremental lines follow the surface of 
the dentine. "As the centre of the area is approached, this regularity is much 
interfered with, some of the lamellas being discontinued, others greatly thickened, 
while the field, taken in its entirety, suggests anything but regularity in the lay- 
ing down of the different strata. Magnified 60 times, a. Granular layer of 
Tomes. {Photomicrograph by Norman Broomell.) 

much thinner at the cervical than at the apical region: in 
adult cementum their width is greater, and they are usually 
more numerous in the latter than the former situation 1 (Norman 
Broomell). 

The term "Incremental lines" was introduced by Salter, 
("Dental Pathology and Surgery," 1874), and includes the 

1 "The Histology of Cementum." The Denial Cosmos, Vol. xl., p. 706, 1898: 
also Broomell and Fischelis' "Anatomy and Histology of the Mouth and Teeth," 
P- 3Si, 1917. 



THE CEMENTUM 87 

laminations sometimes found in enamel (but not the brown 
striae of Retzius, or Schreger's lines), the contour lines of Owen 
in dentine, and the layers of stratification in cementum. 

Stohr ("Text-book of Histology," Wurtzburg, 1914) says that 
" Cementum contains typical bone cells enclosed in large lacunae 
which connect with one another through canaliculi. In young 
teeth Haversian canals are absent, but in old teeth they occur 
in the outer layers near the apex of the root." These are alto- 
gether erroneous statements. And Sir Ernest Schafer ("The 
Essentials of Histology," 19 16) figures on page 303 a drawing 
after Sobotta, which gives an entirely false impression of the 
structure of normal cementum. There are no lacunae in the 
normal tissue: the illustration is that of hyperplasic cementum. 

(iii) Perforating Canals and Fibres 

In close juxtaposition to the band of homogeneous tissue 
which borders the dentine, and running at right or acute angles 
to it, in adult normal cementum, there can be commonly seen 
thick bundles of connective tissue fibres and broad irregular 
canals. In this way the homogeneous layer is bounded inter- 
nally by the granular layer, externally by groups of perforating 
canals and fibres. The former are few and irregularly curved 
in an outward direction, and may occasionally extend half- 
way through the thickness of the cementum. The author has 
found some of them supplied with tiny filamentous branches. 
The latter on high magnification are seen, in sections prepared 
by Weil's process, to consist of myriads of bundles of blackish 
strands. They are short and thick, and remind the observer 
of the odontogenetic fibres of dentine matrix. Their outer 
extremities may enter the canaliculi (Fig. 71). 

Black considered them, and seemingly with sound scientific 
reasonableness, to be the calcified or semi-calcified remains 
of the "principal fibres," of the periodontal membrane. 

Sharpey's fibres, penetrating from without, may be noted 
in some sections of cementum where the hard and soft parts 
have been prepared and preserved in situ. They are very 
shor. straight or slightly curved bundles of fibrils, the main 



THE DENTAL TISSUES 




Fig. 71.- — Longitudinal section of cementum. Prepared by Weil's process. 
Shows the perforating canals and fibres. Magnified 420 times, c. Cementum; 
G. Granular layer; h. Homogeneous layer; d. Dentine. 




Fig. 72. — Sharpey's fibres of cementum. Magnified 800 times. Unstained. 
c. Cementum slightly hyperplasic. 



THE CEMENTUM 



8 9 



characters of which agree with white fibrous tissue, while 
some may be of the nature of elastic tissue. They are identical 
with the perforating fibres in the lamellae of bone. In cemen- 
tum they occupy the interiors of slightly truncated canals. 




Fig. 73. — Perforating fibres passing from the outer margin of the first- 
deposited cementum outwards "until the next incremental line is reached, at 
which point they gradually disappear, but recur in the succeeding lamella." 
Magnified 1,000 times, a. Primary or oldest layer of cementum. {Photomicro- 
graph by Norman Broomell.) 



As will be seen, Sharpey's fibres are entirely distinct struc- 
tures compared to the perforating fibres described above. 

Normal cementum is non-vascular; but there would seem 
to be, in the majority of cases, fine protoplasmic fibrils which 
traverse the boundary line between dentine and cementum. 

Norman Broomell, in the excellent study already men- 
tioned, would recognise in the tissue under consideration 



go 



THE DENTAL TISSUES 



three zones or layers, not always discernible but fairly con- 
stant. The inner, first-formed, is granular, unbroken, and 
continuous with the granular layer; the intermediate con- 
tains many lacunae; and the outer or youngest exhibits many 
sinuous incremental lines. As the tissue becomes more fully 
calcified the lacunae disappear, and the zone possesses many 




ogt- 

neous 

.yer of 

dentine 



Fig. 74. — Fibres passing in a direction almost parallel to the surface, and 
towards the apex of the root. Magnified 300 times. (Photomicrograph by 
Norman Broomell.) 



of the histological characters of the oldest layer. Tomes 
describes this last layer in thick cementum as a "glassy film, 
denser than the subjacent portions," and considers it closely 
similar to the globular formations characteristic of dentine in 
an early stage of development. 

Underwood, in "Aids to Dental Anatomy and Physiology," 
p. 49, 1902, said: "The outermost layer of cementum is struc- 
tureless: . . . when young, globular forms may be traced 
in its substance." s 



THE CEMENTUM 




Fig. 75. — Fibres springing from the granular layer of Tomes, at regular 
intervals, and penetrating the cementum at right angles to the incremental lines. 
Magnified 500 times. A. The circumferential fibres of Broomell. {Photomicro- 
graph by Norman Broomell.) 




Fig. 76. — Structureless cementum of a deciduous tooth. Prepared by grinding. 
Unstained. Magnified 200 times, d. Dentine; c. Cementum. 



92 THE DENTAL TISSUES 

It is, however, perfectly obvious that he still inclined to the 
belief that normally this tissue contains lacunae and cana- 
liculi. 

Cementum in deciduous and supernumerary teeth is 
relatively thinner than that of the permanent series. It is 
nothing more than a very narrow, structureless band (Fig. 
76). 



CHAPTER VI 

STRUCTURAL MODIFICATIONS OF THE ENAMEL, 
DENTINE AND CEMENTUM 

Microscopical Elements in t the Enamel of: (i) Rodcntia; (ii) 
Sirenia. (iii) Tubular Enamel, (iv) Plici-dentine ; (v) Vaso- 
dentin^; and (vi) Osteo-dentine. Cementum. 

Students of comparative anatomy need not be reminded 
that the subject is full of interest with regard to the modified 
forms of teeth, not only in number and shape but also in size 
and function. It is not surprising, then, that the minute 
structure of the masticatory organs of the lower vertebrates 
not infrequently differs very remarkably from that of man. 
As was hinted in Chapter III., enamel may be found, in some 
instances, clear and structureless, in others, presenting a most 
complicated pattern. Here will be briefly considered the 
chief variations in the histology of the enamel, dentine and 
cementum met with in the vertebrates. Tomes' "Manual of 
Dental Anatomy" will ever remain the standard work on the 
subject, and to this and to Sir Richard Owen's "Odontography" 
readers are referred for elaborated details. 



ATYPAL VARIATIONS OF ENAMEL 

Among Mammalia, the Order Rodentia supplies many in- 
stances of modification in structure of this tissue. These varia- 
tions may be a provision on the part of nature to render 
the free surface and incisive margin of the teeth particularly 
strong. Taking the Families in their proper anatomical order, 
brief reference can only be given to the histology of the enamel 
of (i) the Muridce, mice, rats, &c; (ii) Castoridce, beavers; 
93 



94 



THE DENTAL TISSUES 



(iii) Soricidce, squirrels; (iv) Hystricidce, porcupines; and (v) 
Leporidce, rabbits and hares. In Rodentia, generally speaking, 
the large incisors are frequently pigmented a deep orange 
colour. According to Tomes, the colour is situated in the 
substance of the enamel itself. 

Enamel invests the anterior and lateral aspects of the teeth 
and is thicker in the former than in the latter situation. 




Fig. 77. — Vertical section of a persistently growing scalpriform tooth of a 
rodent. Prepared by grinding. Stained with borax-carmine. Magnified 240 
times. Shows striation of enamel rods. e. Enamel; d. Dentine; a. Amelo- 
dentinal junction. 



(i) In the rat the straight columns are arranged in a parallel 
direction, and are placed at an acute angle with the surface of 
the dentine. This is seen in the accompanying photograph 
(Fig. 77). Each rod is not only very striated but is also deeply 
indented, and by making serrations with its neighbours 
renders the tissue remarkably dense and difficult to fracture. 

(ii) The enamel of the beaver exhibits a lattice-like arrange- 
ment of the rods. Longitudinally cut, the enamel rods are 
"inclined upward towards the apex of the tooth, at an angle 
of 60 deg., then, after passing through about half the thickness 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES 95 

of the enamel, they turn up abruptly again, so that they are 
approaching parallelism with the dentine, here making an 
angle little less than 30 deg. with it. It follows from this 
that no transverse section can show very plainly the direction 
of the rods in both parts of their course. The most instruc- 
tive transverse section is one cut parallel with the layers near 
to the dentine; this will plainly show the successive layers 
passing to the right and to the left just as in the squirrel; 
but the yet-more-inclined fibres of the outer half of the enamel 

will then be cut across obliquely As regards the 

decussation of the rods of ultimate layers, it is similar to that of 
the Soricidce, but it differs in the laminas being slightly flexu- 
ous instead of pursuing perfectly straight lines" (Tomes). 

(iii) An apparent division into inner and outer portions 
is exhibited in the enamel of the squirrel. Here, the rods 
are continuous through all the thickness of the tissue, but, 
running in different directions when viewed either vertically 
or horizontally, produce a complex pattern. 

"In the former they leave the dentine at right angles to 
its surface, and after traversing two-thirds of the enamel, 
suddenly bend, and form an angle of 45 deg. with their original 
course: in the latter, they are arranged in horizontal layers, 
each layer a single column in thickness. In alternate layers 
the rods pass to the right and to the left, crossing those of 
the next layer at right angles, and thus making a pattern of 
squares in the inner two-thirds of the enamel. In the outer 
third, where the rods bend abruptly upwards, those of super- 
imposed layers no longer pass in opposite directions, but are 
all parallel; in fact, no longer admit of distinction into alter- 
nate laminas" (Tomes). 

(iv) Individually, flexuous rods are found in the enamel of 
the porcupine, the courses of which are not confined to one plane. 
At the periphery of the tooth the rods run in a parallel direction. 

(v) Parallel, slightly curved enamel columns are constant 
in the teeth of hares. 

In the Order Sirenia, of which the manatee is an example, 
the enamel rods run in a perfectly straight course, and are not 
flexuous. This is therefore a very simple type. 



90 THE DENTAL TISSUES 

Simpler variations still are found in Pisces. Some Families, 
e.g., eel, hake, etc., have a homogeneous type of enamel which 
exists as a tiny free structureless point on the dentine. The 
majority of fishes, however, probably possess a system of 
tubes which pass either partially or wholly through the enamel. 

Tubular Enamel 

GENERAL CHARACTERISTICS 

Definition. — As the expression implies, the enamel, instead 
of being a solid mass of rods and basis-substance, presents a 
tubular structure. 

Origin. — The tubes are produced through the failure of 
calcification of the central zones of the rods formed by the 
ameloblasts of the enamel organ. 

Distribution. — A class characteristic of Marsupials (except 
the wombat), but. found also in some examples of Pisces, e.g., 
Sargus, barbel, porbeagle shark, and certain Insectivora (So- 
ricidce) and Rodentia, such as jerboa, etc. 

HISTOLOGY 

The chief point of interest is the presence of a system of 
tubular canals in the substance of the tissue. These may be 
very extensive and numerous, or very short and few; and be 
confined to the inner or cortical aspects of the enamel or in 
its intermediate portions. 

It has already been shown that in human enamel dentinal 
tubes often cross the amelo-dentinal junction, to end either 
ccecally or else in the enamel-spindles. But in addition to 
these, comparative anatomy furnishes many instances where 
other tubes occur. Dentinal tubes pass across the boundary 
and run into the enamel in marsupials {e.g., kangaroo). 

In many fishes, the passage of these tubes from the dentine 
takes place, but the canals grow smaller in calibre as they 
approach the enamel cortex, which, however, they do not 
reach. Tomes describes and figures {op. cit. p. 56) enamel 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES 



07 



from the tooth of a fossil shark in which the tubes pierce both 
the inner and outer zones. In Sargus Ovis, and Cestracion 
(Heterodontis) they likewise penetrate from the surface. 

The tubes are found in the longitudinal axes of the enamel 
rods, not in the basis-substance; and their courses are generally 




Fig. 78. — Sagittal section of incisor-like tooth of Sargus Ovis, showing tubular 
enamel. Prepared by grinding. Unstained. Magnified about 10 times, e. 
Enamel; d. Dentine. 



fairly straight and parallel. In Sargus, nevertheless, after 
peripheral penetrations and running at right angles with 
the surface, they suddenly bend at an obtuse angle with their 
course (see Fig. 78). 

It is difficult to offer a satisfactory explanation of the pres- 



9 8 



THE DENTAL TISSUES 



ence of these enamel tubes, but the opinion expressed by 
Tomes is, no doubt, correct. 

Thus (p. 59) he writes: "If all enamel, in its development, 
passes through a tubular stage, then these are merely arrests 
of complete development and perpetuations of a stage which 
is transitory in placental mammals." 

It is probable that tubular enamel is atavistic. 




Fig. 79. — Same as preceding. Magnified 240 times. 



Paul's views are not in accord with those of Tomes. In 
an article in The Dental Record, p. 496, 1896, this author 
observed: 

"If we admit the general principle that all spaces or tubes 
in enamel are between and not within the rods, then the 
structure of genuine tubular enamel seems less difficult to 
understand. It is clear that any imperfect approximation 
of enamel cells must leave spaces between the rods which 
can only be filled with an indefinite intercellular substance, 
or possibly by further prolongations of dentine matrix, and 
in neither case is it likely that such intercolumnar matter 
would become calcified; because on the one hand, it is too 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES 



99 



far removed from the influence of the odontoblasts, and on 
the other, because the calcifying energy of the ameloblasts 
is almost entirely expended upon their own internal petri- 
faction. I would therefore suggest that tubular enamel is 
an enamel in which there is an excessive amount of inter- 
cellular substance only imperfectly calcified, and much as it 
looks like tubular dentine, it is really formed on an exactly 




Fig. 80. — Transverse section of a rostral tooth of Pristis. Prepared by grinding. 
Stained with coloured collodion. Magnified about 10 times. 

opposite plan. The one is a negative and the other a posi- 
tive picture. In dentine the cells occupy the tubes, and the 
intercellular substance becomes the solid calcified matter; 
in enamel the tubes are represented by the intercellular sub- 
stance, whilst the cells become the solid calcified matter." 

But it must be confessed that Paul's remarks seem hardly 
quite apposite in this connection, based as they are on the 
probably incorrect hypothesis that odontoblasts form dentine 
matrix. The syllogism he uses is faulty, inasmuch as the 
premises are not generally accepted, and are open to a dif- 



IOO THE DENTAL TISSUES 

ferent interpretation. In his studies of marsupial enamel, 
Howard Mummery's opinion coincides with those of Paul, 
who investigated the subject from the point of using the enamel 
of man. His conclusions (Phil. Trans. 1914) are that "The 
prisms (sic) are the first portions of the enamel which undergo 
calcification, that these prisms (sic) are arranged in layers corre- 
sponding to the rows of ameloblasts cells and that the spaces 
between the layers are calcified subsequently and cement the 
tissue together." 

VARIETIES OP DENTINE 

Tomes has classified Mammalian dentine as ortho-den- 
tine (Hard, or unvascular dentine, sufficiently described in 
Chapter IV.), plici-dentine, vaso-dentine, and osteo-dentine. 
This is considerably more correct than that found in the writings 
of Owen, who somewhat confuses the two last-named varieties. 
Thus the older palaeontologist described vaso-dentine as being 
composed of coarse channels containing cells, vessels, and nerves 
of the pulp — obviously the osteo-dentine of the latter author. 
By limiting the expression vaso-dentine to those forms in which 
blood-vessels only permeate the dentine, Tomes has cleared 
away many conflicting conceptions. 

Plici-dentine 

Definition. — "An ordinary dentine with its surface folded up 
and wrinkled into a greater or less degree of complexity" 
(Tomes). 

Histologically considered, the dentine is hard, and unchan- 
nelled except by tubes which radiate, as usual, more or less 
at right angles to the pulp cavity. 

If a pulp chamber be merely indented externally, or if 
portions of the dentine are somewhat invaginated, or the pulp 
itself, instead of being simple in outline, has several prolonga- 
tions, no longer does a cylindrical pulp cavity result, but one 
with folded outlines. 

This obtains in the teeth of the Selache maxima (Basking 
shark), or Ichthyosaurus. 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES IOI 




Fig. 8i. — Transverse section near base of tooth of Anarrhicas lupus. Shows 
the plicated outlines of the dentine. Magnified 45 times. From a specimen in 
the collection of Sidney Spokes. 




Fig. 82. — A form of Plici-dentine. Transverse section of tooth of an extinct 
crocodile (Telcosaurus). Prepared by grinding. Unstained. Magnified 240 
times. 



I02 THE DENTAL TISSUES 

In Lepidosteus the upper part of the tooth consists of a simple, 
single pulp chamber, with plicated walls, while at its base there 
are several pulp chambers running longitudinally, and variable 
in size, each always having radiating dentinal tubes. The 
peripheral pulp cavities run in straight lines in a centrifugal 
direction. And so also in Anarrhicas lupus (Fig. 81). 

If these straight lines become twisted or curved or branched, 
a much more complex pattern is produced, as in the extinct 




Fig. 83.— The sar 



as the preceding. Longitudinal section. Magnified 240 

times. 



reptiles Labyrinthodon, Lcptognathus, and Dendrodus Bipor- 
catus; also an extinct Crocodile Teleo-saurus. 

Many teeth are composed of groups of vertical denticles 
or primary pulp canals with radiating dentinal tubules. The 
periphery of each system occasionally blends almost imper- 
ceptibly with those of neighbouring denticles. Thus a regular 
pattern is seen in both horizontal and vertical sections. The 
teeth of the rostrum of Pristis, of an extinct hippopotamus, 
Myliobates, Zygobates, and others reveal this. In the first 
condition each dentinal system is permeated with fibrils from 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES 103 

the central pulp. The dentine is harcTand unvascular, but not 
plicated. 

Vaso-dentine 

Another variety of this dental tissue, in which, broadly 
speaking, there are no tubules as such, is vaso-dentine. As 




Fig. 84. — Sagittal section of an intermaxillary tooth of Anarrhicas lupus 
Prepared by grinding. Unstained. Magnified about 10 times. The mass of 
tooth is occupied by vaso-dentine. 

the term implies, it is a vascular dentine. Extending outwards 
through the matrix is a series of moderately sized canals or 
channels of nearly uniform calibre throughout, each filled 
with a capillary from the pulp. 



104 THE DENTAL TISSUES 

The channels run in the same direction as the tubes in hard 
dentine — that is, radially. A little below the free surface of 
the tooth their distal extremities are formed by loops, the 
convexities of which are outwards. Dried sections some- 
times show thorn-like processes, running laterally from^the 
vascular canals (see Fig. 85). 




Fig. 85. — Vertical section of tooth of Merlucius vulgaris (Hake). Prepared 
by Weil's process, with the substitution of Golgi's method of staining. Magni- 
fied 250 times. Shows the vascular channels in the dentine, with their so-called 
"thorns," and the laminated matrix of the dentine. 



The matrix of the dentine itself is slightly laminated. 

Vaso-dentines are found in many fishes — hake, cod, Sargus, 
flounder, haddock, &c, in the former of which the canals are 
numerous, in the latter scanty. The dentine of the first-named 
is tubeless. The teeth of manatee and Megatherium possess 
vascular canals as a normal characteristic. 

Osteo-dentine 

In its general histological configuration, osteo-dentine 
closely approximates to that of compact bone, but the inter- 
stitial and peripheric lamella? are wanting. Its irregular 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES 105 

spaces are analogous with the medullary canals of compact bone. 
They contain, however, in this case, not medullary tissue, but 




Fig. 86. — Vertical section of base of tooth of Carcharias. Osteo-dentine 
Magnified 50 times. 



pulp with round osteoblastic cells lining the walls in young 
developing specimens. 



io6 



THE DENTAL TISSUES 



Osteo-dentine is found in the teeth of fishes, of which it may 
form the whole or part, as in the photomicrograph (Fig. 86). . 

In typical instances, when longitudinally cut, it is made up 
of more or less parallel trabecular, which extend through the 

A 




Fig. 87. — Longitudinal section of ankylosed tooth of Esox lucius (Pike). 
Prepared by the Author's process. Stained with Ehrlich's acid haematoxylene. 
Shows osteo-dentine. The full growth of the osteo-dentine is incomplete, a 
few elastic rods remaining in the centre of the tooth. Magnified about 10 times. 
a. Apex of tooth composed like the periphery of the dentine; b. Bone of attach- 
ment; e. Elastic rods, or uncalcified trabecular; p. Pulp in situ; m. Soft tissues of 
the mouth. 



substance of the tooth, traversing the pulp tissue and dividing 
it into great numbers of pulp cavities. There is no very 
regular tube system, otherwise the result of this sub-division 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES 107 

into minor pulp cavities would be a flat form of plici-dentine 
in which the denticles are placed side by side in a regular 
and uniform manner. 

In the osseous matrix lacunae are sometimes found, and the 



\iCM 



Fig. 88. — Vertical section of tooth of Esox Indus. Prepared by decalci- 
fication. Pulp tissue'not retained in situ. Stained with borax-garmine. Mag- 
nified 40 times, o. Osteo-dentine; b. Bone of attachment. 

dentine is more or less permeated by minute canaliculi. Many 
variations from this type exist. The structure of the teeth of 
Lamna (Porbeagle shark) may be cited as an example. Tomes 
(op. cit. p. 99) describes it as follows: "In an osteo-dentine me- 
dullary canals of varying size run, with a direction, roughly 
speaking, parallel to the long axis of the tooth, anastomosing 



108 THE DENTAL TISSUES 

with one another; and from their sides wavy bundles of fine 
tubes radiate but do not run far; that is to say, its dentinal 
tubes do not radiate from any one central pulp chamber, but 
from an indefinitely large number of canals." 

Recent Classification of the Varieties of Dentine 

Rose has recently attempted a new classification of Dentine, 
and his communications to dental science, in these as in other 
matters, are always interesting. Thus he distinguishes: — 

(i) Pure or Ortho-dentine, a term suggested by von Kupffer, 

(ii) "Trabecular," or rod-like dentine, 

(iii) Osteoid dentine, 

(iv) Bone dentine. 

(i) Pure dentine is a hard tissue with a smooth surface, of 
unilateral growth, being developed under an epithelial sheath 
or enamel organ. 

This includes the following sub-divisions : — 

(a) Tubular dentine, i.e., normal tissue containing the 
canals for the reception of protoplasmic cell processes, 

(b) Vitro-dentine, i.e., tubeless and structureless, with no 
protoplasmic filaments whatever, 

(c) Vaso-dentine, i.e., containing blood-vessels. 

(ii) Trabecular dentine, corresponding to the "osteo-dentine" 
of Tomes, is a new term introduced by Rose, who defines it as 
"a hard tissue with numerous short protoplasmic-bearing 
dentinal canals, capable of increase of growth in all directions, 
but not growing immediately beneath, or in dependence upon 
an epithelial sheath." 

This variety is probably formed similarly to intra-mem- 
branous ossification of bone. Thus, in the interior of the 
pulp cavity, at an early period of development, arise rod-like 
tracts of closely aggregated round cells. Within these tracts 
or columns, the first rudiments of structureless dentine are 
laid down exactly after the manner of the formation of the 
first layers of compact or cancellous bone. Single columns 
grow and increase in length and diameter. They thicken at 
the expense of the pulp tissue, become fused in places, and ex- 



STRUCTURAL MODIFICATIONS OF THE HARD TISSUES IO9 



hibit fine-tubed dentinal systems. Ultimately with the com- 
pletion of the growth of the tooth, instead of there being 
one pulp cavity, there are many wide tubular canals containing 
pulp tissue radiating in every case in a centrifugal manner. 

E 




Fig. 89. — Vertical section of the cervical region of a molar tooth of Didelphys 
Virginiana (Opossum). Prepared by grinding. Unstained. Magnified 45 
times, d. Dentine; e. Enamel; c. Normal lacunated cementum. 

The first formed parts of the rods are structureless, and these 
are designated by this author as Vitro-trabecular dentine. 

(iii) Osteoid dentine is a hard tissue growing in all directions ; 
contains no protoplasmic enclosures; sometimes forms pure 
bone tissue and sometimes trabecular dentine. 

(iv) Bone dentine, or Osteo-dentine, is a transitional form, 
between bone on the one hand and dentine on the other; 



IIO THE DENTAL TISSUES 

contains both bone corpuscles and dentinal tubules, each 
carrying a protoplasmic fibril. 

MODIFICATIONS OF CEMENTUM 

Little need be recorded about this. It is sufficient here to 
point out that the normal cementum of some of the Marsupial 
mammals (e.g., the opossum, see Fig. 89), does contain promi- 
nent well-shaped lacunas and canaliculi. Not only are the 
spaces of fairly uniform size, and the canaliculi of regular calibre 
and length, but the arrangement in layers or series is regularly 
parallel. Deposition of the tissue with inclusion of cemental 
corpuscles has, doubtless, proceeded without deviations from 
the original and earliest formed layer. The cementum, there- 
fore, forms naturally a thick coating to the roots of the teeth, 
and comparison with the lacunated hyperplasic cementum 
of the teeth of man cannot fail to have a striking and convincing 
effect on the mind of the astute and experienced observer. 



CHAPTER VII 

THE DENTAL PULP 

Microscopical Elements: — (i) Odontoblasts; (ii) Pulp cells proper; (iii) 
Fibrous stroma; (iv) Basal layer of Weil; (v) Arteries, Veins, and 
Capillaries; (vi) and Nerves. 

GENERAL CHARACTERISTICS 

Definition. — The soft, vascular, and sentient organ which 
occupies the central portions of teeth, being naturally bounded, 
on all sides, by dentine, which thus constitutes its cavity. 

Origin. — In Man and Mammalia it is the ultimate forma- 
tion of the dentine papilla, which is itself derived from the 
stomodoeal parietal mesoderm (somatopleur). 

Distribution. — All the calcified teeth of fishes, reptiles, and 
mammals have pulps. 

Macroscopical Appearances. — A soft, thin, flattened, whitish 
organ, with, occasionally, lines of pink running in a longitu- 
dinal direction if removed from its bony cavity before post- 
mortem changes occur. 

Its measurements in upper permanent adult teeth are as 
follows : — 

Greatest average width, sagittally and midway between 
apex of root and incisive or occlusal edge: First incisors, 1.5 
mm.; canines, 2.5 mm.; first premolars, 3.5 mm.; second pre- 
molars, 3.8 mm.; and molars, 5 mm. 

Greatest average length: First incisors, 19 mm.; canines, 
19.5 mm. (in a coronal direction, 23 mm.); first premolars, 
17 mm.; second premolars, 15 mm.; molars about 15 mm.; 
third molars, 11.5 mm. 



THE DENTAL TISSUES 




Fig. 90. — Longitudinal section through the cornual region of a young adult 
molar, the dentogenetic zone of which is on the point of calcification. The pulp 
is in situ. Prepared by the Author's process. Stained with Ehrlich's acid 
hasmatoxylene. Magnified 80 times, d. Dentine; p. Pulp tissue in cornu of 
tooth; d.z. Dentogenetic zone; o. Odontoblasts; b.l. Basal layer of Weil; b. 
Blood-vessels; N. Nerve bundles. 



THE DENTAL PULP 



113 



o 



Fig. 91. — Transverse section of an adult canine, with the' pulp in situ. 1 
Prepared by the Author's process. Stained with rubine. Magnified 45 times. 
d. Dentine; p. Pulp tissue proper; o t . Oi. 03. Odontoblast layer; A. Artery; 
v. Vein; M. Myelinic nerve bundle. 

x The narrowest diameter of the pulp in the section of which Fig. 91 is a photo- 
micrograph, measured 1.5 mm.; the widest diameter 3.35 mm. 



ii 4 



THE DENTAL TISSUES 



For purposes of description it is advisable and convenient 
to arbitrarily divide the pulp as well as the pulp chamber 
into the (i) coronal region — the most distal portion which 




Fig. 92. — Similar to the prece 
hasmatoxylene. Magnified 45 times. 
of Weil. 



but stained with ^Ehrlich's acid 
Blood-vessels in the basal layer 



projects into the crown of the tooth; (ii) the cornual region 
indicating one of the pointed or rounded extremities of the 
coronal region, (iii) the cervical; and (iv) the radicular regions — 
that is, at the neck and in thejoots of teeth respectively. 



THE DENTAL PULP 115 

HISTOLOGY 

The dental pulp is a delicate connective tissue 1 consisting 
of ramified cells imbedded in a slightly fibrous stroma and 
granular transparent basis substance, and is plentifully sup- 
plied with blood-vessels and nerves. 

Examined microscopically the several parts of the dental 
pulp of man exhibit objects of profound interest and impor- 
tance — of interest because so many debatable and debated 
theories circle around the cells and nerves, and of importance 
because on its integrity depends the life-history of the tooth. 
To systematically study them, the subject may be divided 
into descriptions of (A) its cellular elements, (B) its connective 
tissue stroma or framework, (C) its vascular supply, and (D) its 
nervous svstem. 



The Cellular Elements 

The cells of the dental pulp fall naturally into two classes: 
of these the former is the more important when full growth 
of the organ has taken place; the second during its develop- 
mental periods. A cursory examination of an adolescent or 
adult pulp shows that two kinds of cells stand out clearly 
distinct from each other — the peripheral prominent layer, 
the so-called odontoblasts, and the central, smaller, less con- 
spicuous pulp cells. The latter should be termed "Odonto- 
blasts," inasmuch as it is their function to build the matrix 
of dentine; while the former might be known as "pulp cor- 
puscles," signifying different work. See footnote on page 50, 
also the Appendix (page 327). 

As bearing upon this point the statement of Rose may be 
recalled. He says (loc. cit.): "The odontoblasts of pure 
dentine have, like the formative cells of 'trabecular' dentine, 
quite the appearance of osteoblasts. If one wishes further to 
distinguish odontoblasts from osteoblasts, and chooses not to 

1 It is said to be similar to the jelly-like connective tissue of the early embryo, 
which in the case of the umbilical cord persists, and is called the jelly of Wharton. 



Il6 THE DENTAL TISSUES 

make use ot the commonly employed term 'scleroblasts' 
introduced by von Klaatsh, new and concise definitions must 
be introduced. It would be commendable in the future to 
define only those dentine-forming cells that range themselves 
along an epithelial sheath as 'odontoblasts,' quite indif- 
ferently, whether one refers to multangular cells below or cy- 
lindrical cells above. Hence the word 'odontoblasts' belongs 
only to those formative cells of true dentine. The formative 
cells of 'trabecular' dentine and bone tissues, which have never 
had any connection with an epithelial sheath should, on the 
other hand, be defined as osteoblasts." 



(i) The Cells of the Membrana Eboris of Kblliker or the 
Odontoblasts 



All along the periphery of young or mature pulps, arranged 
like a palisade in a single row two or three cells deep, is a col- 
lection of large, columnar epitheloid cells. This layer is most 
marked at the coronal portion of the pulp, and becomes appre- 
ciably less distinct at the cervical portion, while in the region of 
the root it is practically invisible. It is most clearly seen 
in the developing teeth of kittens and other embryos, as well as 
in complete sagittal longitudinal sections of young and adult 
human pulps, although in the latter the columnar character of 
the layer has disappeared. In transverse sections, too, .this 
layer is visible, and it is not difficult to say with accuracy from 
which portion of the pulp the particular section has been taken. 
A closer inspection reveals the fact that the membrana eboris 
is composed of cells — the so-called odontoblasts, a term sug- 
gested by Waldeyer in 1870, and generally adopted since that 
time. In young pulps it consists of a single row of cells; in 
adult specimens several rows. These cells are of the utmost 
interest and moment. They will be described with regard to 
shape, size, relationships, structure, processes, and analogies. 

(a) An odontoblast, generally speaking, in its very earliest 
phase of development, is represented by a large oval nucleus, 



THE DENTAL PULP 









1 1-7 



^V 



Fig. 93. — The structure of the pulp tissue. Prepared by Weil's process 
Magnified 250 times. 









Fig. 94,— Same as the preceding. Prepared by the Author's process. Mag- 
nified 250 times, c. A Capillary. 



THE DENTAL TISSUES 




Fig. 95. — Odontoblasts on the surface of the pulp. Prepared by fixing and 
hardening in formalin and alcohol, and cutting on an ether-freezing microtome. 
Stained with chloride of gold. Magnified 250 times. To show the enormous 
length of the dentinal processes of the cells. 




Fig. 96. 



-Young odontoblasts from a developing tooth germ. Magnified 250 
times, o. Odontoblasts. 



THE DENTAL PULP 119 

devoid of visible protoplasm (Paul). 1 It may be recognised 
without difficulty, when about one-fourth its normal size. "It 
then consists of a large oval nucleus situated at its extreme 
base, with a short pyramid of protoplasm reaching towards the 
surface, and displacing the fibres of the surface pulp cells on 
either side. At this time it possesses no dentinal fibre, merely 
ending in a blunt point, though no doubt some delicate invisible 
protoplasmic processes are given off." 

Later on, but while still young, and during its period of 
greatest activity, an odontoblast is a large bipolar, nucleated, 
epitheloid cell, more or less columnar in shape. This varies 
considerably in the same specimen, and ranges from that of 
a mere thin cord with bulbar terminations to that of a pear 
or banana, as Underwood 2 has likened it. Many cells are 
carrot-shaped, many caudate. Some are short and thick, some 
long and thin; some have, as is well known, square dentinal ends, 
others rounded extremities. But it would appear that those 
found in fully grown pulps are more or less pyriform in shape, 
while those in older specimens are reduced often to a thin fibrous 
bundle. A point worthy of notice is the fact that cells in the 
same plane — the same section — differ much in conformation. 
Where the pulp is constricted or flattened laterally, there the 
odontoblasts are thick and short; in the place where the pulp 
is broadest, however, they are long and thin. Moreover, in the 
latter situation, in adult pulps, they have enlarged extremities, 
that near the dentine sometimes presenting a stellate appear- 
ance, with the processes leaving the cell from the points of the 
star. Most probably this has been occasioned by shrinkage of 
the cells through the action of reagents. Often this dentinal 
extremity is triangular, often rounded. The central portion 
or body of the cell is very considerably attenuated and cordlike 
(see Fig. 97). 

In teeth having cylindrical pulp cavities this diversity in 
shape is scarcely appreciable, and probably does not exist. 

It may be said that the same remarks apply also to the pulps 
of fully formed deciduous teeth. 

'■"A Contribution to the Histological Study of Dentine." Trans. Odonlo. Soc. 
of Great Britain, p. 129, 1899. 

2 "Aids to Dental Anatomy and Physiology," p. 25, 1902. 



THE DENTAL TISSUES 




Fig. 97. — Similar to Fig 91. The odontoblasts marked o? in that photo- 
graph. Magnified 750 times. To show the peripheral processes extending into 
the dentinal tubes as the dentinal fibrils. 




Fic e 98. — Similar to Fig. 91. The odontoblasts marked 03 in that photo- 
graph. Magnified 750 times. 



THE DENTAL PULP 121 

An odontoblast is said to have no limiting membrane. 

Pathological conditions, such as inflammation, suppura- 
tion, or calcareous degeneration of the pulp do not seem, at 
first, to affect the shape of the odontoblasts: this rule obtains 
in all normal and abnormal examples. But later their forms 
become profoundly altered. 

(iS) With regard to size, odontoblasts vary considerably, the 
coronal cells being larger and more marked than the radicular 
cells of the pulp. This change in size corresponds in a measure 
to the length and width of the tubules, with which they are 
closely associated. The largest cells in an embryonic tooth- 
germ — viz., those under that part of the dentine which is cov- 
ered by enamel, and called, for the sake of brevity, the coronal 
part of the pulp — have a diameter of 10 to 15/x, and if they be 
compared to adult cells in the same situation, the latter will 
be found to vary from 25 to 30^ in length, with a breadth of 
about 5/x. Waldeyer 1 gives the size of adult odontoblasts, 
but does not compare them with developing cells — a point of 
importance which seems to have been overlooked. 

It seems reasonable to suppose that this diversity of size 
would account for the increase of calibre of the fibril (and 
therefore tubule) as it approaches the pulp. Paul (loc. tit. 
p. 134) mentions that at the period of time when the dentinal 
matrix has reached a depth of }4o mm., the odontoblasts 
are very long, but remain about 7.7^ in width. In the ox 
they may attain the length of 50/1. According to Kolliker, 
the stratum of the membrana eboris, in an adult pulp, measures 
from 41 fj, to 83 ju in thickness; the odontoblasts themselves 
being 25^ long, and 4m to 4.5^ broad. 

(7) Relationships to surrounding structures: — 

The author, in a paper written in 1889, showed that these 
cells are not packed closely together, but are separated by 
wide visible spaces, which in certain cases are filled with a 
"homogeneous substance, and small, round, and angular 
cells." It is necessary to add that this is the case in develop- 
mental pulps, there being only a slight amount of intercellular 
tissue in most adult specimens. There are visible also in many 

1 Strieker's Histology, Vol. 1, 1870, p. 476. 



122 THE DENTAL TISSUES 

instances, fine delicate spiral fibrils of connective tissue stretch- 
ing into the dentine between the odontoblasts, in addition to 
the already mentioned structures. These fibres are not nerves, 
but form what may be termed the "supporting fibres" of the 
pulp. Reference to this point will again be made later on 
(page 130). 

The long axes of the odontoblasts are approximately in the 
same direction as that of the tubules — a fact well brought out 
in transverse sections of pulp cut in situ, and best observed in 
its narrowest part. 

In some sections, the cells are separated some distance by 
a gap, in which a capillary loop may lie quite close up to the 
dentine, and also pulp matrix — viz., delicate intercommuni- 
cating fibres. And in young pulps, in which dentine matrix 
is still being produced, many of the cells have attached to 
their distal ends lines of "transitional tissue" which Paul 
calls "collars." An odontoblast "collar" or shoulder is thus 
often seen, and was described by the earlier investigators as 
a lateral or median process of the cell. Mature cells do not 
possess it, only those of earlier stages of growth exhibiting it. A 
"collar" nearly always adheres to the dentine matrix, but very 
often to the cells themselves; is more highly refractile than 
any other part of the cells, and is the only portion in which 
they are in mutual contact. It is important to notice, how- 
ever, that a "collar" is not part and parcel of the odontoblast. 
It is pierced by its dentinal process. It is probably derived 
from the pulp matrix, and really consists "of a delicate net- 
work of pulp fibrils woven about the necks of the odonto- 
blasts upon which the secretion of the latter is poured and 
solidifies to form the dentine matrix." This is the interpre- 
tation supplied by Paul; but while the author agrees with the 
histological appearances just described, he cannot see his way 
clear to accept Paul's exposition or statement as to the lime- 
bearing functions of the odontoblasts. 

(<5) In structure, the cytoplasm of the odontoblasts possesses 
a coarse degree of granularity, which does not disappear on the 
addition of a weak acid, and is apparently unaffected by glyc- 
erine, and certain other chemical re-agents. The distal ends 



THE DENTAL PULP 1 2 7, 

of the cells when young are apparently clear and homogeneous, 
the granularity being confined to the lower four-fifths. In 
transverse section, this granularity is due to either (i) a coarse, 
deeply staining reticulum or spongioplasm, (ii) metaplastic 
inclusions, or to (iii) the presence of numerous translucent 
globules (? of first-formed calcoglobulin). The author has 
failed to see the clear zone in adult odontoblasts, and considers 
that the spongioplasm becomes coarser through thickening of 
the nodes of the spongioplasm as time goes on, and the amount 




Fig. 99. — Section of tooth germ before the surface cells of the pulp have 
undergone any differentiation. Magnified 250 times. (Photomicrograph by 
Paul.) 

of the hyaloplasm is proportionately diminished. Hence he 
again differs from Professor Paul in his belief that the clear 
zone is due to calcoglobulin. 

The nucleus of an odontoblast is large, ellipsoidal, and promi- 
nent, and is situated at the basal extremity of the cell. Its 
wall is well-defined, and its karyoplasm pronounced. Occa- 

1 In this connection a remark by Professor Schafer ("Quain's Anatomy" vol. I., 
part II., p. 174, 1898), is of profound significance: "It would seem that the 
presence of certain inorganic substances, and especially calcium, is essential to 
the life, and therefore to the functions of protoplasm; but in what manner the 
lime may be combined with the organic basis of the living material, remains as 
yet quite undetermined." 



124 



THE DENTAL TISSUES 




Fig. ioo. — A later stage than Fig. 99. Shows surface pulp cells becoming 
arranged in a fairly regular layer, with their chief processes directed towards the 
ameloblasts. Magnified 250 times. {Photomicrograph by Paul.) 




Fig. 10 1. — Shows complete evolution of surface pulp cells They have pro- 
duced a superficial fibrous layer, and their nuclei are now in a "resting" state. 
The odontoblasts have not yet appeared Magnified 250 times. (Photomicro- 
graph by Paul.) 



THE DENTAL PULP 




Fig. 102. — Shows the line of "transitional tissue" along the top of the odonto 
blasts. At one place it stretches across a gap between two cells caused by the 
intervention of a blood-vessel undergoing degeneration Magnified 250 times. 
(Photomicrograph by Paul.) 




- ^m^ [ 



Fig. 103. — A very thin section of odontoblasts, showing the pulp fibres in- 
vesting them, and ending in the "transitional tissue" forming the shoulder or 
collar of each cell. Magnified 340 times. (Photomicrograph by Paul.) ' 



126 THE DENTAL TISSUES 

sionally nucleoli may be found. The nucleus is usually placed 
at the centripetal end of the cell as has been already stated; but 
Paul has shown that it may be found in the middle, and occa- 
sionally quite at the distal end, where its long axis lies trans- 
versely to the cell. In this latter case, however, it must 
not be forgotten that the odontoblast itself is very short, or 
has been cut obliquely so as to appear short. If a cell was 
lying a little out of the level plane of its neighbours, in a ver- 
tical section, the nucleus would probably appear higher in 
the body of the cell than usually obtains. Paul thinks that 
it exhibits an exhausted condition, and has ceased to grow. 
An odontoblast may have two nuclei in the same cell, a "con- 
dition by no means uncommon," and, rarely, atrophied nuclei 
have been observed by Paul in the dentinal fibril, just beyond 
the transitional tissue. These appearances are interpreted 
by him as being due to coalescence of two odontoblasts, 
the lower cell reinforcing and rehabilitating the degenerated 
upper odontoblast. 

(e) The processes. — These cells are remarkable for their polar 
offshoots, which may be classified as (i) central or basal; and 
(ii) peripheral or dentinal. 

Of these, the first named are most easily observed in sections 
when ordinary stains are used, but the latter cannot be so clearly 
demonstrated unless special methods of staining with hasma- 
toxylene or gold chloride are adopted. Carmine and rubine and 
a few aniline dyes show them also. 

(i) The peripheral poles of the odontoblasts, extend into 
and enter the tubules of the dentine, and are here called dentinal 
fibrils. In some cases they are bifurcated: several fibrils may 
emanate from one cell; and nothing else can be seen entering 
the tubule. Boll 1 has counted as many as six processes belong- 
ing to one cell. 

The length of a peripheral process of an odontoblast may 
measure 4 or 5 mm. It thus may measure in extent one 
hundred and fifty times the length of the cell body. This fact 
alone raises an odontoblast to a much higher level than the usual 
cells of a mesodermic tissue. As a matter of fact, the dentinal 

1 "Untersuch. der Zahnpulpa." Archh. fur Mikrosk. Anal., p. 73, 1868. 



THE DENTAL PULP I 27 

fibril issuing from an odontoblast renders this cell one of the 
most extraordinary in the body. In the human economy 
no more remarkable cellular units are known microscopically 
than the cell bodies of certain neurones, which may possess, as 
processes, axones extending to a distance varying from 3^ or 
4fx to one metre in length. Second to these are the truly 
marvellous odontoblasts whose processes — the dentinal fibrils — 
may measure 4 mm. There can be no doubt whatever that 
these wonderful cells possess high functional possibilities. 

(ii) It is no difficult task to demonstrate the basal offshoots of 
the odontoblasts. They are exceedingly thin and may inter- 
communicate with each other. This, however, is not at all 
satisfactorily proved. They present no varicosities of surface, 
are not swollen or twisted, and take the stain less deeply 
than other portions of the pulp tissue. They are invisible in 
young developing cells. Special stains, such as Golgi's, 
Stroebe's, or methylene blue have failed up to the present time 
to trace back these central poles to the terminations of the 
nerves of the pulp. 

According to Magitot, 1 the basal processes of the odonto- 
blasts are continuous with the branches of large reticulate 
cells, situated as a layer, beneath them. These latter cells are 
placed in direct line with the nerve terminations (see diagram, 
Fig. 127). In this manner, the sensibility of the dentinal fibril 
might be accounted for. Recent workers have not, however, 
corroborated Magitot's views, and his deductions, in the light of 
more modern research, would seem to be incorrect. 

In the dental pulp of the ox, these basal processes assume a 
large size. If an incisor is removed from the jaw of an ox, 
immediately after the animal has been slaughtered, and then 
broken longitudinally in a vise, the basal poles may be demon- 
strated in a few minutes, while still fresh. A small piece of the 
membrana eboris is removed and teased in salt solution; while 
carmine or chloride of gold clearly stains the long processes. 

Aitchison Robertson 2 has studied these offshoots in the ox, and 

1 Journal de V Anatomic de M. Charles Robin, Paris, 1881. 
2 "On the Relation of Nerves to Odontoblasts, and on the Growth of Dentine." 
Trans. Roy. Soc. of Edinburgh, p. 323, 1891. 



128 



THE DENTAL TISSUES 



he reports that "odontoblasts were seen which had become 
separated from the other cells, and had drawn out along with 
them their internal or root process. This was in some cases of 
great length, and could be traced for some distance into the 
pulp. In other cases, part of the dentinal fibril still remained 
attached to one extremity of the separated odontoblasts, while 




Fig 104. — Portion of surface of the pulp teased in potassium anhydrochro- 
mate solution. Shows the very long central process belonging to each odonto- 
clast and entering the substance of the pulp. The odontoblast has fallen off 
in many cases, and leaves the central process projecting like a fine hair or nerve 
fibre. (After Aitchison Robertson.) 







[05. — Apparent direct continuation of the root process of the odonto 
blasts with the axone of a nerve. (After Aitchison Robertson.) 



from the other extremity, the long internal root process was 
seen extending into the pulp." The processes sometimes 
measured even twelve times the length of the odontoblast cell, 
and in some instances passed into groups of nerve fibres, amongst 
which they apparently ran for some distance before they ac- 
quired a myelinic sheath. This author significantly ob- 
serves: "I am convinced that the central processes of the 
odontoblasts become continuous with the nerve fibrils. . . . 
The long central process seems to become the axis-cylinder of a 



THE DENTAL PULP 1 29 

nerve fibre, which gradually acquires a primitive sheath in which 
the medullary or white substance slowly accumulates, till an 
ordinary medullated nerve results. ... It is very difficult 
to say whether all the odontoblasts send in their long processes 
to join the nerve fibres." 

It is a histological fact that odontoblasts possess processes 
running towards the pulp; but it has not been proved, in spite 
of Robertson's work, that they are the direct continuation 
of the pulp myelinic nerve-fibres. 

Their existence is doubted by Hertz ("Untersuch. iiber 
den feineren Bau und die Entwickelung der Zahne," in Vir- 
chow's "Archives," Bd., 37, 1866) and by Paul. 

($■) There is a certain amount of analogy existing between 
the odontoblasts, and certain epitheloid cells, found in the 
olfactory regions of man and animals, in the ganglionic layer 
of the retina, and the auditory cells of the macula lutea of the 
membranous labyrinth. Their processes are somewhat similar, 
their structure identical, their shape modified only by the 
mutual apposition of neighbouring cells. 

(2) The Other Pulp Cells 

The cells of the pulp proper, viz., those situated in the 
central portions of the tissue, differ in size and shape during 
the various stages of the growth of that organ. In developing 
teeth they are large, and have rounded angular or spindle- 
shaped outlines. In short, they partake of the nature of em- 
bryonic cells generally. Their nuclei are large, prominent, 
oval or lenticular, contain karyosomes and chromatin, and are 
devoid of nucleoli. Near the superficial portions of the pulp 
they are very loosely held in the reticulum by the connective 
tissue stroma; and here, more spindle cells are visible. 

In adult teeth, the pulp cells are chiefly stellate or angular 
in shape, with numerous branches. Their number is greater, 
as a rule, than the ordinary round cells; but cells of any de- 
scription are comparatively few. The branches are long and 
multiplied, and interlace with one another, giving the pulp 
somewhat the appearance of a mucoid tissue. Fewer cells 
exist in the radicular region of the organ. A few insignificant- 

9J 



130 THE DENTAL TISSUES 

looking odontoblasts are found; but the mass of the pulp seems 
composed of bundles of thick and thin connective tissue fibres 
and cells running in all directions. 

The morphology of the individual cells is best studied in 
fresh pulps which have been teased-out in physiological salt 
solution, and suitably stained. 

B 

The Connective Tissue Stroma 

Extending throughout the pulp in every direction, like an 
exceedingly minute net, is the connective tissue stroma or 
scaffolding in which the cells are imbedded. This framework 
serves two purposes, as an imbedding material for the pulp 
cells, and as a support to sling up the soft delicate organ in its 
bony casing, in much the same way as marrow is supported 
in the medullary cavities of bone. The fine fibres appear some- 
times to enter the dentinal tubules, but they are most often 
seen attached to the free margin of the matrix of the dentine, 
where, most likely, they are in reality the odontogenic fibres. 
The author in 1893 was the first to draw attention to those 
" supporting fibres " of the pulp. They are generally recognised 
by their spiral appearance, and have recently again been 
studied by Von Korff (Archiv. fiir Micros. Anat., 1907) and 
Studnicka (Anat. Anzeiger, 1907). It is probable that these 
connective tissue fibres are considered by Howard Mummery 
{Proc. Roy. Soc. Medicine, 191 2) to be the terminations of the 
myelinic nerve fibres of the pulp. 

In the sub-odontoblast region of the pulps of adult teeth the 
basal layer of Weil is seen. This, first described by the late 
W. A. Weil, of Munich, 1 in his monograph on the Dental Pulp, 
consists of a distinct clear layer of fibres with a great scarcity 
or even absence of cells. In describing it, he wrote: "The 
layer contains no cellular elements or nuclei; it appears rather 
as a web of extremely fine fibrils, which do not run perpen- 
dicularly through the layer, but running obliquely towards the 
deeper layers, interlace with one another in a crosswise direc- 

1 "Zur Histologic der Zahnpulpa." Leipzig, p. 55, 1887. 



THE DENTAL PULP 



131 






Mi 



$ 






WM 



\ 



m 




Fig. 106. — The dental pulp. Prepared by the Author's process, and stained 
with Ehrlich's acid hcematoxylene. Magnified 750 times, a. Artery; c. 
Capillary; v. Vein; p. Pulp tissue proper; F. Fasciculus of myelinic nerve fibres. 



132 THE DENTAL TISSUES 

tion. ... It may be said, with perfect security, that they 
arise from the projecting basal ends of the odontoblasts. It is, 
however, surprising that these offshoots do not follow the axial 
directions of the odontoblasts, but turn sideways to one direc- 
tion or another, and thus form the crossings." 

The basal layer measures at the coronal part of the pulp 
0.025 mm. in diameter, and gradually becomes diminished in 
size, until it no longer exists in the radicular region. 

This statement is corroborated by Partsch, 1 of Breslau, 
and deserves great attention. 

Further, Howard Mummery 2 refers largely to this in a 
recent paper, where he says: — "According to my experience 
the layer is not visible in young teeth in the situation of the 
rapidly depositing dentine at the open, uncompleted end of 
the root." And it may be added, that the author has repeatedly 
observed it in the mature pulps of deciduous and permanent 
teeth as well as in certain pathological conditions; but never in 
young growing teeth. Professor Paul has, however, noticed 
"a clear zone of tissue just beneath the most actively growing 
young odontoblasts." He declares: — "It seems to me, after 
many careful examinations, that the appearance is not due to 
the presence of a specialised tissue, but is simply owing to a 
rarefaction of the pulp preceding the active extension of the 
odontoblasts, which are of course progressing inwards through 
the pulp matrix." 

Regarding the exact nature of the basal layer, it is a difficult 
matter to decide. It is certainly fibrous; but whence the fibres 
come and go, and whether the whole layer is an artificial product 
or not is as yet undecided. 

Weil himself considered that the fibres were undoubtedly 
continuous with the odontoblasts, and might thus be a means 
of communication between them and the nervous system of 
the pulp. He never was able to prove, however, that these 
delicate fibres were amyelinic nerves. Repeated attempts 
at differential staining to ascertain if they were of a nervous 
character have failed. A stray capillary may cross the layer 

1 Deutsche Monatsschrift fiir Zahnhcilkunde, p. 322, 1892. 
2 Journal of British Dental Association, p. 779, 1892. 



THE DENTAL PULP 



133 



and get into the spaces between the odontoblasts. Howard 
Mummery does not believe that all the fine fibres are in con- 
tinuity with the odontoblasts; many of them penetrate through 
the layer and enter the dentine matrix. 

Its existence as a true histological structure is doubted by 
Ebner and Rose. 

von Ebner says: — "The odontoblasts are attached to the 
dentine by means of the dentinal fibrils — they cannot, there- 
fore, when the inner portions of the pulp shrink up (through 




Fig. 107. — The pulp in situ. Prepared by the Author's process, and stained 
with Ehrlich's acid haematoxylene. Magnified 250 times, b. The basal layer 
of Weil; o. Odontoblasts; d.z. Dentogenetic zone. 

the action of reagents used in the Koch-Weil balsam process) 
be very well torn away; but the layer immediately under the 
odontoblasts will seek to approach the centre of the pulp, and 
before it comes to a rupture, the tissue elements which form 
the connection of the odontoblast layer with the pulp lying 
beneath, will be very strongly stretched. These tissue elements 
are chiefly fibres, and in this way a layer of fibres can be arti- 
ficially produced which before was non-existent 

Dr. Weil shows that from the tissue of the pulp, rich in cells, 
which is found beneath the membrana eboris, numerous fibres 



134 THE DENTAL TISSUES 

penetrate toward the odontoblasts. But that these fibres, 
in life, exist as a special basal layer cannot be proved by Dr. 
Weil's method." 

And thus also Rose. 

But Howard Mummery considers that the facts of the non- 
distortion of blood-vessels in the layer, as also its absolute 
disappearance at the growing extremity of the roots of teeth 
with large apical foramina must be taken into account, and 
disprove the theory of shrinkage of the pulp. 



The Vascular Supply 

The pulp is freely vascularized by branches which are 
derived from the Posterior Dental, Infra-orbital and Mandib- 
ular divisions of the Int. maxillary artery. 

They enter the teeth through the apical foramina of their 
roots, generally as one large trunk, or as three or more small 
ones. Shortly after their entrance into the pulp, the vessels 
branch repeatedly, become smaller in calibre, until near the 
surface they form a simple capillary network which may 
measure 8fi to 12 n in width. It may be stated in general 
terms that there is no collateral circulation in the pulp. In 
this respect the condition resembles that which obtains in 
the terminal blood-vessels of the brain, the arteria centralis 
retince of the eye, and in a lesser degree also in the walls of the 
heart. 

During the period of development the vascular system 
covers a large area of the dentine papilla. The main arterial 
trunk, proceeding in a longitudinal direction through the 
centre of the tissue, decreases in diameter very gradually, 
till near the edge of the dento-genetic zone, when it almost 
suddenly and rapidly becomes narrower, and is ultimately 
lost in a dense capillary plexus. The branches have the 
peculiarity that very often they issue at or about right angles 
with the main vessel (see Plate I). 

In adult pulps, this angular method of division is not so 



THE DENTAL PULP 



135 



evident; the larger vessels are located chiefly in the axial 
portion, whence numerous branches pass in all directions. 

In the cornual regions many anastomatic capillary loops 
have their convexities directed towards the dentine. As a 
rule, these capillaries extend as far as the basal layer of Weil; 
but occasionally, as has been already mentioned, one or more 
may cross, and pass between the odontoblasts (Fig. 92). 




Fig. 108. — A sympathetic nerve fibre running along the wall of a capillary of the 
dental pulp. Highly magnified, n.f. Nerve fibre; e.c. Endothelial cell of cap- 
illary wall; N. Nucleus of pulp cell. Preparation and photomicrograph by Dr. 
H. Box, Royal College of Dental Surgeons, Toronto. 

The arteries vary in size, in different pulps, but a main trunk 
may measure about 83 /x in width, while the diameter of the 
lumina of the capillaries is roughly about 8/j. 

The former are accompanied, not only by their respective 
veins, but also by fasciculi of myelinic nerves, which run 
side by side, sometimes so closely that nothing but a few 
connective tissue fibres and cells intervene between the outer- 
most portion of the external coat, or tunica adventitia, of the 
artery, and the perineurium of the latter. 

By selective staining it is possible to demonstrate the sym- 
pathetic nerve fibres which are distributed to the middle and 
outer coats of the vessels. 



136 THE DENTAL TISSUES 

Properly stained horizontal sections of pulps reveal in a 
most beautiful manner both the approximate number of 
blood-vessels and also their differences in structure. In 
typical canine pulps, cut crosswise through the cervical region, 
the author has counted 10 of the former. The typical veins, 
several of which were just macroscopically visible, exceeded 
this number by 14, while the capillaries were practically count- 
less. 1 

Histologically considered, the vessels of the pulp differ 
very considerably. 

The Arterioles. — Structure. — The wall of each small artery 
consists of three coats, viz., the tunicce intima, media and 
adventitia, the first-named being indistinguishable, except 
under high magnifications, and the media being very marked. 

(i) Tunica intima. — Here is found, forming the lining of 
the lumen of the vessel, a flattened layer of thin, singularly 
elliptical endothelial cells, each having a round or oval nucleus. 
When the blood corpuscles have not been retained in situ 
in the section, the cells may be sometimes seen to project 
into the lumina. External to the endothelial lining is an 
attenuated double wavy line, continuously circling the artery. 
This is known as the elastic layer of the inner coat, and it is 
made up of numerous longitudinal, closely arranged yellow 
elastic fibres, (ii) The Tunica media is composed mainly 
of plain muscular tissue, which makes this coat the thickest 
and most prominent of all. It is arranged circularly round the 
vessel, and its component parts are made up of unstriated 
muscle fibres with elongated nuclei. The elastic tissue of the 
larger arteries is wanting in this coat in the vessels of the pulp, 
(iii) The Tunica adventitia, consisting of areolar or connective 
tissue fibres and cells, with nuclei placed in the long axes of the 
cells, represents the outer coat of the artery. These fibres 
and cells, too, run circularly round the vessels and blend inti- 
mately with the connective tissue fibres of the pulp. 

1 These figures are introduced in this connection, in order to supply the reader 
with some idea as to the numbers that may be computed, i.e., to demonstrate 
that the arteries of the pulp are not counted in hundreds, but in tens. It is 
obvious that the numbers given are never constant. 



THE DENTAL PULP 137 

Nervi vasorum are present in this coat. They belong to the 
sympathetic nervous system. 

The Veins differ from the arteries in the fact that the size of 
the middle coat is greatly reduced, and the endothelial cells are 
shorter and broader. Otherwise they resemble the arteries. 
In sections, they are easily differentiated from the other blood- 
vessels in having a very much greater diameter. They are 
non-collapsible in the pulp, have no valves, and retain the 
rounded outlines of their walls. This is doubtless due to their 
strong support by means of the stroma which permeates the 
pulp tissue. 

The walls of the Capillaries are exceedingly delicate, being 
formed by a single layer of endothelium, which is a continuation 
of the endothelial lining of the arteries, on the one side, and the 
veins on the other. The smallest capillary walls may consist of 
only two or three of such cells, which, in this case, are curved to 
form the interior of the tube. The nuclei are marked and the 
karyoplasm pronounced (see Fig. 106). 

There are no traces of any organized lymphatic system in the 
dental pulp. That is to say, evidences of the existence of 
endothelially-lined lymphatic capillaries or vessels are wanting. 
Pericellular and intercellular lymph spaces or tissue spaces are 
everywhere apparent, as also are those around the blood-vessels 
and nerve bundles. The pulp is saturated with lymph which is 
derived from the blood plasma, as an exudation from the capil- 
laries. It permeates the pulp tissue and exudes into the den- 
tinal _tubules around the odontoblast processes. It, however, 
does not pass into lymphatic vessels, and does not leave the pulp 
by any such channels. Yet Schweitzer, in an elaborate article 
{Arch. f. mikr. Anat., 1907) claims that, by careful injection, he 
has succeeded in demonstrating tufts of lymphatic capillaries 
in the coronal portion of the pulp, which collecting the lymph of 
that neighbourhood, conveys their contents into one or two wide 
lymphatic vessels which issue from the apical foramina of the 
teeth in company with the blood-vessels. The dental pulp is 
one of those few parts of the body which is devoid of any lym- 
phatic system. 



138 THE DENTAL TISSUES 

D 

The Nervous System 

As eliciting the closest attention on the part of many thinkers 
and writers, as presenting a truly fascinating and profoundly 
interesting field of speculation, as affording ample opportunities 
for most brilliant work in original research, the study of the 
nervous sytem of the dental pulp may claim to be, of all dental 
histological subjects, of the first importance, instruction, and 




Fig. 109. — The plexus of Raschkow, teased out, and stained with chloride of 
gold. Magnified 250 times. 

value. One is completely astonished at the mass of literature, 
old and new, which has been devoted to it. Its bibliography is 
manifold, and in itself would furnish, if gathered in one volume, 
most illuminating reading. Yet in spite of the earnest labours 
of one half-a-century, it is amazing to recall the fact that while 
so much is known about it, so much is still unknown — the actual 
methods of the peripheral distribution of the myelinic (medul- 
lated) nerves being buried in obscurity. True, that some 
of the earlier histologists solved most carefully in suo modo 
this particular and difficult problem; true, that modern 



THE DENTAL PULP 



139 



methods of preparing the hard and soft tissues for micro- 
scopical examination have shed new light on it; it still remains 
to be noted that the anatomical data and physiological 
principles involved in the phenomena which give rise to pain 
in the teeth — the whole innervation of the pulp — the direct 




Fig. 1 10. — Similar to Fig. 106. To show six nerve bundles cut transversely. 
Prepared by the Author's process. Stained with rubine. Magnified 750 times. 
c.T.c. Connective tissue fibres and cells; c. Capillary; M. One of the nerve 
bundles. 

course by which sensation is conducted from the dentine or 
enamel to the cortical areas of the cerebral hemispheres cannot 
be considered satisfactorily determined. But its capability of 
solution is unquestionable. 

Here an attempt will be made to describe the chief recognised 
facts, and some arguments in this nebulous matter. The nerv- 
ous system of the dental pulp consists of the peripheral pro- 



14° THE DENTAL TISSUES 

longations and terminations of certain cerebro-spinal ganglionic 
neurones emanating from the upper and lower sensory nuclei in 
the medulla and fourth ventricle, and passing through to the 
Gasserian ganglion. They are cellulipetal, and while con- 
stituting the peripheral axones of receptive afferent neurones, 
they are essentially the distal telodendria of the peripheral sen- 
sory neurones. They terminate structurally like the teloden- 
dria of the other ordinary sensory nerves, and probably arborize 
about the odontoblasts on the surface of the pulp and do not 
penetrate the dentinal tubules. The blood-vessels of the pulp 
are under the trophic control of fibres of the sympathetic 
system. It will be convenient to consider the subject under the 
following headings: The myelinic nerves, their (i) method of 
distribution, (ii) structure, and (iii) terminations in (a) fishes, 
(b) reptiles, (c) mammals. 

(i) Method of Distribution. — Emerging from the "indifferent 
tissue" of the periodontal membrane, in company with the main 
arterial trunks, and entering the apical foramina of the teeth, the 
bundles of myelinic and sympathetic nerve fibres pass collec- 
tively into the pulp, in lines directly corresponding to its long 
axis. There are thus several funiculi colligated into sheaves; 
and without undergoing much appreciable diminution in num- 
bers, they extend into the soft tissue, and maintain a more or 
less parallel direction with the outlines of the dentinal walls. 
The nervous trunks pass, like long, straight or very slightly 
wavy lines, in this way, for some considerable distance, and 
then begin gradually, as they approach the parieties of the pulp, 
to break up into smaller fasciculi; until, when close to the basal 
layer of Weil, the original bundles are represented only by two 
or more nerve fibres running side by side. In many instances, 
the bundles stretch up to the sub-odontoblast region, and then, 
according to Rose and Gysi ("Portfolio of Microphotographs of 
Dental Histology," 1895) very suddenly burst forth in myriads 
of minute scopiform strands. The result is the formation of an 
interlacing of fibres — the plexus of Raschkow (see Fig. 109). 

In every case the chief nerve fasciculi run alongside the larger 
blood-vessels, and in their areas of distribution follow them 
closely, and, in the case of the sympathetic fibres, penetrate 
their external coats. 



THE DENTAL PULP 



141 




-Myelinic nerve fibres, teased out. Stained with osmic acid. Magni- 
fied 850 times, r. A node of Ranvier. 




Fig. 112. — Similar to the preceding. Magnified 800 times. 



142 THE DENTAL TISSUES 

Towards their distal arborisations they become in places lobu- 
lated or varicose, a condition which, according to Schafer, 1 is 
occasioned by pressure or traction on them, causing the soft 
matter "to accumulate at certain points, whilst it is drawn out 
and attenuated at others." In addition to these occasional 
dilatations, and near their peripheral distribution they divide 
into branches — each component part participating in the divi- 
sion. By oft-repeated sub-division the fibres become much 
smaller. 

(ii) In structure, the myelinic or white nerve fibres correspond 
with those found elsewhere in the cerebro-spinal system of man, 
except in one particular, and that is with regard to size. The 
individual fibres in the pulp vary from 1.5/x to 3/z in diameter. 
Kolliker has measured them. His figures are: In diameter, 
the large trunks in the radicular part of the pulp, are 62 n to 8m; 
their constituent elements 3/x to 6^; and their primitive fibres 
2-5M to 34M- 

Each consists of (a) the axis-cylinder of Purkinje; (j3) the 
medullated sheath of Schwann; and (7) the primitive sheath 
or neurilemma. 

(a) The axial fibre, or axis-cylinder process, or more shortly 
the axone, extends without interruption through the whole 
length of the nerve fibre, from its origin in the cell body in the 
cerebrum to its ultimate ramifications near the membrana 
eboris. It is to-day an almost certain fact that the axone is 
always a direct prolongation of a branch of a nerve cell, ex- 
tending far away from its origin, but yet in perfect conti- 
nuity with it. Max Schultze in 1837 2 observed that the axone 
consists not of a single cord or thread, but is a complex structure 
made up of many fibrils, ("primitive fibrillae") imbedded in 
fine granular material. Obersteiner told Gowers 3 that he had 
counted as many as fifty such primitive fibrils in a single 
axone,'' each fibril having a separate and distinct path of 
conduction. 

1 "Quain's Anatomy," Vol. II., part I., 191 2. 
2 Vide Strieker's "Histology." 
3 "The neurone and its relation to disease." British Med. Journal, Nov. 6th, 
1897. 



THE DENTAL PULP I 43 

(j3) The myelin sheath, or white substance of Schwann, is 
easily identified in sections of the pulp when stained with osmic 
acid, the action of which is to render the fatty matter (which 
contains lecithin) of the myelin a dark grey or black colour. 

The medulla is continuous, but presents here and there 
breaks in its continuity. These constrictions are known as 
the nodes of Ranvier. Occurring at nearly equal intervals, 
they divide the fibre into internodes. The white substance 
has undergone a certain amount of shrinkage at a node, and 
is quite transparent, but in addition there is present a finely 
granular stroma rendered evident through refraction by the 
fatty matters which are usually found in it (Fig. in). 

The nodes of Ranvier, when treated with various stains, 
exhibit other markings. In this way, a weak solution of silver 
nitrate reveals the crosses of Ranvier — in which the cement 
joining two internodes, and a small portion of the axone are 
affected, and also sometimes Fromman's lines — a cross-stria- 
tion of the axone at the node; and a i per cent, solution of 
osmic acid, minute nodes on the primitive fibrils of the axone 
with the black constricting ring of Ranvier placed outside 
(van Gedoelst). 

Further sub-divisions in the medullary sheath are found in 
the form of oblique slits passing outwards from the axone to 
the neurilemma. These are called "incisures," and are ren- 
dered apparent by the use of osmic acid and picro-carmine. 
They split up the internodal myelin into a series of short 
lengths or "cylinder cones," the bevelled end of one cone 
fitting accurately into the opposite similar end of the neigh- 
bouring cone. 

In addition to these various histological structures in the 
myelinic sheath of nerves, there exist also, when suitably stained, 
radial virgate striations, as well as a more-or-less-coarse 
reticulum. 

(7) The primitive sheath or neurilemma forms the external 
covering of white nerve fibres. It is an exceedingly delicate 
homogeneous membrane which passes over every node of 
Ranvier, and possesses in the mid-distance of an internode a 
large flat nucleus. At a node, the neurilemma is probably 



144 THE DENTAL TISSUES 

discontinuous with the axone, because of the intervention of the 
annular constricting band of Ranvier. 

A horizontal section of the pulp stained carefully with 
osmic acid or haematoxylene or other stains displays the 
nerve bundles cut across. Collectively examined they show 
the endoneurium — fine connective tissue septa passing in 
between the individual nerve fibres, as processes of the peri- 
neurium which surrounds the fascicule itself. Several fas- 
ciculi are invested by the epineurium. These coverings — endo- 
neurium, perineurium, and epineurium — are continued to the 
ultimate terminations. In the finest branches they are re- 
duced to a mere connective tissue sheath, the sheath of Henle. 

The sympathetic nerve fibres — fibres of Remak — are the 
axones of neurones belonging to the sympathetic system, being 
distributed to the blood-vessels as vaso-dilators or vaso-constric- 
tors. They are amyelinic, measure i/x to 2\x in diameter, 
consist of axone and neurilemma, and terminate as telodendria 
composed of naked axones. 

(iv) Peripheral Terminations of the Nerves 

In order to pave the way to some knowledge of the 
anatomical distribution of the free extremities of the nerve 
fibres in the dental pulps of man, it will be expedient and 
instructive to note how the nerves end in the pulps of the 
teeth of fishes, reptiles, etc. 

(a) In Pisces 

Here the evidences as to the exact mode of the terminal 
arborization of the sensory nerve fibres are quite clear, thanks 
to the splendid labours of Gustav Retzius. 1 By Golgi's method 
of staining, he succeeded in positively demonstrating in the 
teeth of Gobius and Gasterosteus, anatomical conditions which 
agree in all essential points. Definite types of nerve-branching 
were observed. 

1 "Biologische Untersuchungen," Neue Folge, iv., v. and vi., 1892, 1893, and 
1894. 



THE DENTAL PULP 



145 



The amyelinic nerve fibres arising from a dense plexus in 
the soft tissues in which the teeth are situated, pass into the 
pulp and spread out thickly to form free endings in that 
tissue, extending upwards towards the coronal region, and 
abundantly giving off lateral branches with free terminations. 
The extreme cornu of the pulp is not supplied with nerves. 
(For illustrations of this condition see Figs. 113 and 114.) 




Fig. 113. Fig. 114. 

Figs. 113 and 114. — Longitudinal sections of the teeth of Gobiits. Golgi's 
stain, d. Dentine; n. Nerve fibres, ending in free terminations, close under the 
dentine. {After Retzius.) 



(0) In Reptilia 

Retzius was able here, to trace the nerves quite easily, still 
using Golgi's method. In Lacerta agilis he describes them as 
rising, in the first place, from the middle of the pulp. He writes 
(pp. 65 and 66, Vol. iv). "In the pulp may be seen the con- 



146 



THE DENTAL TISSUES 



nective tissue which also contains blood-vessels, a black thread 
apparently consisting of nerve fibres matted or closely pressed 
together. This thread rises upwards, and gradually gives off 




Fig. 115. — Longitudinal section of tooth of a larva of the Salamander maculata. 
Golgi's stain. N. Nerve fibre. (After Relzius.) 

branches which extend partly towards the side, and partly 
upwards. These enter the odontoblast layer, and pass between 
the cells, as a rule, to the upper surface of the pulp, there to end 



THE DENTAL PULP 



147 




Fig. 116. — Tooth of larva of Salamander maculata with the surrounding oral 
mucous membrane. Golgi's stain, n. Amyelinic nerve fibre, branching and end- 
ing free in the pulp ; p. Nerve fibre in the circumdental tissues, ending free in e. the 
surface epithelium. (After Retzius.) 



148 THE DENTAL TISSUES 

directly under the dentine in free extremities, which here and 
there are swollen into knots. In transverse section these fibres 
penetrate the odontoblast layer, and reach the inner surface of 
the dentine, there to end free after a short ramification. The 
penetration of nerve fibres into the dentine was nowhere 
observed." 

The larvae of Salamander Maculata and Triton Cristatus 
provided suitable material for further tracing the amyelinic 
nerve fibres. In these preparations, after their entrance 
into the pulp, the nerves divide dichotomously, and, branch- 
ing upwards, end partly in the side of the pulp tissue, and 
partly close under the surface of dentine. The fine varicose 
branchlets rise about half-way up the tooth, but never pass to 
the upper end of the pulp (p. 41, Vol. v.). "All branches end 
freely, spreading out in different parts of the pulp. Most of 
them apparently end close under the dentine or near its inner 
surface, but never penetrate into its substance or into its canals." 



(7) In Mammalia 

The precise method by which the sensory nerves finally 
terminate in the pulp of the teeth of man, constitutes one of 
those histological puzzles which yet remain unsolved; and 
even to-day, it is absolutely impossible to give a clear and proved 
solution. As has already been hinted, the subject is too vast 
to do more than mention the chief modern theories connected 
with it. 

1. In the teeth of young mice, Retzius in 1894 {op. cit. Vol. 
vi., p. 64) succeeded in staining the nerve fibres, not only every- 
where in the pulp, from the beginning, near the blood-vessels, 
but also in tracing their branches into the odontoblast zone, 
and between these cells to the under surface of the dentine. 
"In vertical sections the fibres, like a string of tiny beads, 
stretch between the odontoblasts to the surface and there end 
free." They often bend round on reaching the surface, and 
run a little way tangentially. In a tangential section they can 
be partially traced under the dentine." 



THE DENTAL PULP 



149 



2. Franz Boll, 1 over fifty years ago, observed fine fibres 
(which he thought were nerves), by means of K2 P er cent- 
solution of chromic acid, in the pulps of rabbits and guinea-pigs. 




Fig. 117. — A vertical section through the tooth of Lacerla agilis. Golgi's 
stain, d. Dentine; O. Odontoblasts; P. Pulp with blood-vessels and N. Nerves 
which branch, penetrate between the odontoblasts, continue their ramifications 
to the upper surface near the dentine, and there terminate. {After Retzius ) 

He used the persistently growing teeth. He traced them to 
places between the odontoblasts, and even between the dentinal 
processes of the odontoblasts which had been detached from the 

1 "Untersuchungen iiber der Zahnpulpa." Archiv.jiir Mikroskop. Anatomie, 
Vol. iv., p. 73, 1868. 



ISO 



THE DENTAL TISSUES 



dentine. Thus he believed that the nerve fibres extend into the 
dentinal tubules. The nature of the fibres first described by 
Boll was most uncertain, and did not present the gemmules or 




Fig. 118. Fig. 119. 

Fig. 118. — Transverse section of tooth of Lacerla agilis. Golgi's stain. 
D. Dentine; o. Odontoblast layer; N. Nerve fibre which passes free to the upper 
surface of the odontoblast layer and there terminates. (After Retzius.) 

Fig. 119. — Vertical section of the upper part of a young tooth of a mouse 
five days after birth. Golgi's stain, e. Enamel with the ends of the dentinal 
tubes projecting into it; d. Dentine with stained dentinal tubes; o.L. Odonto- 
genetic zone; o. Odontoblast ; n. Amyelinic nerve fibre passing between the odonto- 
blasts. [After Retzius.) 





Fig. 120. Fig. 121. 

Fig. 120.' — Vertical aspect of odontoblasts having between them two ulti- 
mate branches of a fine varicose nerve fibre. From the pulp of a molar tooth 
of a rabbit. Prepared by staining with methylene blue fixing in ammonium 
molybdate and mounting in balsam. (After Huber.) 

Fig. 121. — Similar to the preceding figure. Odontoblasts seen end on. The 
nerve termination lies over the cells. (After Huber.) 

beads which Golgi's and methylene-blue methods of staining 
depict upon the axones. 

3. Carl Huber, 1 of the University of Michigan, made use 

1 "The Innervation of the Tooth-pulp." The Dental Cosmos, vol. xl., pp. 803 
etseq., 1898. 



THE DENTAL PULP 



151 



of the mandibular canines and molars of dogs, cats, and rabbits. 
His most satisfactory results were obtained from the pulps of 
rabbits' molars. The method of staining he employed was 
1 per cent, methylene blue in physiological salt solution injected 
into the common carotid during life. He describes the follow- 




Fig. 122. — Amyelinic terminations of the nerves in the dental pulp of a 
Stained with methylene blue. {After Huber.) 



ing interesting histological revelations: — "The medullated, i.e., 
myelinic, nerve fibres approach the lower portion of the pulp 
in one or several relatively large nerve bundles. On reach- 
ing the lower surface of the pulps, these larger bundles break 
up into numerous smaller ones, the latter consisting of eight 
to ten nerve fibres, although larger ones are frequently met 



152 THE DENTAL TISSUES 

with. In the fibrous tissue membrane which covers the under 
surface of the pulp, and which is continuous with the periodontal 
membrane, these smaller nerve bundles form, as the result of 
frequent anastomoses, a plexus of medullated fibres. . . The 
smaller bundles of medullated nerves, coming off from the 
plexus, pass nearly perpendicularly up into the pulp, into 
which they may be traced as small bundles of medullated 
nerves, two to eight or ten in number, to all levels of the pulps, 
some to the very tip. ... On approaching the surface of the 
pulp, the medullated fibres lose their medullary sheath: the non- 
medullated (i.e., amyelinic) terminal branches, after repeated 
division, form a plexus immediately under the odontoblasts. 
They branch and re-branch into long, delicate varicose fibres." 
This plexus is that of Boll, and Raschkow, and others, but 
according to Huber, it is "a plexus only in so far that the 
varicose fibrils cross each other in various directions." 

Huber's observations on the ultimate termination of the 
nerves corroborate those of Retzius. The fibrils given off from 
the plexus just mentioned as being present beneath the odonto- 
blasts, pass up between these cells, and end, as fine beads, 
usually near the free or dentinal end of the odontoblasts. Some- 
times they run tangentially. Huber says that they do not, in 
his opinion, make any connection with the odontoblasts, nor 
with any of the cellular elements of the pulp: and he scouts the 
idea of their entrance into the dentine. 

4. Legros and E. Magitot 1 examined the dental pulps of the 
calf, dog and cat, and concluded that the terminal filaments are 
continuous with ramified cells, situated immediately below 
the odontoblasts, with which they are in immediate communi- 
cation. "There is thus," according to these authors, "a direct 
chain of sensation transmitted from the nerve-ending to the 
dentinal fibril via the branched cells, and the basal processes of 
the odontoblasts, the bodies of these latter and finally their 
peripheral poles" (Fig. 127.) 

The most careful search for such cells in the pulps of Her- 
bivora and Carnivora (including man) has been attended only by 
negative results. 

1 " Morphologie des follicle dentaire chez les Mammiferes." Journal de 
l' Anatomic et Physiologie, 1879. 



THE DENTAL PULP 



153 



5. Oscar Romer, 1 after a great deal of labour and experiment, 
and following on the lines suggested by Morgenstern, used the 
teeth of three-weeks-old kittens, and adopted the intra-vitam 
methylene-blue stain. He enunciated the following, inter 
alia: — 

(i) The nerves of the pulp penetrate, as non-medullated 
filaments, the spaces which intervene between the odon- 
toblasts, reach the zone between these cells and the den- 
tine, and here pass into the interior of the odontoblast 
processes, that is to say, in Kolliker's dentinal tubules. 




Fig. 123. — Diagram of a section through the tooth-germ of a kitten, three 
weeks after birth. Prepared by the intra-vitam method of staining with meth- 
ylene blue; fixing in ammonium molybdate, formalin, and subchloride of plati- 
num; decalcifying in acetic acid, and embedding in celloidin. Shows Romer's 
conception of the passing of the amyelinic nerve fibres into the dentinal 
tubules, a, Dentinal tubes; O, Odontoblasts; n, Fine nerve fibrils going upwards 
out of the pulp, between the odontoblasts to the dentinal tubules in the dento- 
genetic zone. {After Romer.) 



(ii) The chief mass of the nerve filaments radiate out of the 
cornua of the pulp into the dentine; while the other zones 
of the dentine of the crown appear to be poorer in nerve 
branches, and the dentine of the root entirely nerve-less. 

(iii) A greater part of the dentinal tubules widen out at the 
enamel-dentine boundary, into curious partly spindle- 
shaped, partly club-shaped formations which are chiefly 
arranged in very great numbers around the apices of the 
dentinal cusps, and in which, in well-preserved sections, 
small roundish or larger oval corpuscles are perceptible, 

1 hoc. cit. 



154 TH E CENTAL TTSSCES- 

whieh are ofterr arr anged in r a & ai y^ttkerrows; and, witfr 
gold chloride, take an intense stain; and 
(iv) The small corpuscles in the interior of the spindle-shaped 
enlargements of the dentinal tubes may be regarded, with 
great probability, as terminal corpuscles of sensitive nerves 
in the dentine, analogous to the terminal corpuscles of the 
sensory nerves of the skin and the papillae of mucous 
membranes. 
This writer, out of forty-seven drawings in his monograph gives, 
however, only two figures depicting the passage of nerves into 
the dentinal tubules. One is magnified 250 times, and the other 
an amplification of the first, 750 times (vide Tafel iv., Figs. 16 
and 17). In spite of their measurements, (0.25/1 to °-3m), of 
his indefatigable zeal, his earnestness and his precautions, the 
author is unable to agree with the interpretation placed upon 
the appearances presented by the sections, and must distrust 
the drawings accompanying the text. Moreover this writer, 
considering the processes of the odontoblasts as hollow, describes 
sensory nerve fibres as piercing or passing into the interiors of 
these cells. This is entirely erroneous, for nowhere in the body 
do nerve fibres penetrate the walls and mingle with the cyto- 
plasm of cells! Similarly the work of Dependorf (Deutsch. 
Monatss. f. Zahn, 1913) can be at once discounted, for he 
describes and illustrates nerve fibres in the basis substance of 
the dentine! 

6. Aitchison Robertson (op. cit. p. 823) in the pulps of the ox, 
when treated with 0.6 per cent, solution of potassium anhy- 
drochromate for twenty-four hours, found long central proc- 
esses to the odontoblasts, which he believed became continuous 
with the nerve-fibrils. He says (p. 324), "The long central 
process seems to become the axis-cylinder of a nerve fibre which 
gradually acquires a primitive sheath, in which the medullary 
or white substance slowly accumulates till an ordinary medul- 
lated nerve results." His drawings, reproduced in Figs. 104 
and 105, unfortunately convey nothing to the enquiring mind, 
and certainly if they are correct, his assumption is still 
unproved. 

7. Kolliker in i860 (op. cit. p. 300) in the teeth of man, 



THE DENTAL PULP 1 55 

observed that the primitive fibres, which are given off from a 
rich plexus, "form very evident loops," but he did not consider 
them the ultimate terminations. 

8. In specimens of full- term foetuses, presumably Human, 
Bodecker 1 using gold chloride, positively asserts "that an 




Fig. 124. Fig. 125. 

Fig. 124. — Longitudinal section of the dentine of a young Human tooth. 
Stained with osmic acid. a. Axon; n.k. Nerve corpuscle. (After M or genstern.) 
Fig. 125. — Nerve ending in enamel of a young tooth, s. Nerve corpuscle; 
a. Axon. (After Morgenstern.) 

indirect connection of the two "(dentinal fibrils and nerve 
endings) "is established by the intervening reticulum of living 
matter." 

It must not be forgotten, however, that this author believes 
that the dentinal fibrils arise between the odontoblasts, whose 

1 "The Anatomy and Pathology of the Teeth," 1894. 



156 THE DENTAL TISSUES 

role it is to furnish the basis-substance of the dentine. But 
this, as well as many other matters of which Bodecker has 
written, must be accepted with the greatest caution. His 
views are so heterodox, and do not conform in any degree 
with the accepted hypotheses and observations of a great 
number of reputed histologists of various nationalities. 

9. Morgenstern 1 describes in the teeth of man, bundles 
of axones surrounded by their medullary sheaths passing into 
the dentine or enamel. In the former tissue they traverse 
tubules, some of which are smaller and others larger than 
the ordinary tubules. Each canal has in it two axones and 
they terminate either (i) at the cortex of the dentine, or (ii) at 
the amelo-dentinal junction, or (iii) even pass into the enamel. 
In the first-named locality they end in knob-shaped structures 
which may be ellipsoid or pyriform in shape (Fig. 124). In 
enamel they may end variously, as in the dentine, in elongated 
nucleated structures where the axone (a) passes through 
the entire so-called nerve corpuscle to end at its periphery 
(Fig. 125), (/3) terminate on a nucleus of the said nerve corpus- 
cle, or (7) traversing the entire nerve corpuscle, may wind 
itself round one or many nuclei, and end on the last or further- 
most nucleus. 

His chief argument lies in the fact of the black colouration 
found in Golgi-stained preparations, and he has adduced no 
proof that what he has described as nerves are nerves. Thus 
he writes (page 383 op. cit.) "The nerves which appear in the 
dentine when treated by the silver method, show black fila- 
ments of very varied length and thickness. Their intense 
black colour, and different peculiarities — characteristic of nerves 
— leave no doubt of the identity of these fibres with nerve 
filaments. In regard to the wealth or number of nerves, prob- 
ably no one part of the tooth is materially distinguished from 
another. There is, however, probably a distinction in regard 
to the mode of their division and termination. It is the dentinal 
canaliculi which for the most part contain the longer nerve 

1 "Uber das Vorkommen von Nerven in der hartern Zahnsubstanzen." 
Deutsche Monat. fur Zahnheilkunde, p. 436, 1892; also Deutsche Monat. fur Zahn- 
heilkunde, p. in, 1895. 



THE DENTAL PULP 



iS7 




i iiii i ii hi ii i iii FiiiiHiiiiiiiiiiiiiiiiiitnmmi 




Fig. 128. Fig. 129. 




Ell Mill L M 1 1 n 1 1 ITTTTTTTTTTTn EHH 




Fig. 131. Fig. 132. Fig. 133. 

-To show in a diagrammatic manner the various concep- 
tions as to the method of termination of the amyelinic nerve fibres in the pulp. 
Fig. 126, according to Boll; Fig. 127, according to Magitot; Fig. 128, accord- 
ing to Retzius; Fig. 129, according to Aitchison Robertson; Fig. 130, according 
to Romer; Fig. 131, according to Huber; Fig. 132, according to Pont; and Fig. 
133, according to the author, e. Enamel; d. Dentine; b. Limit of pulp tissue; o. 
Odontoblast; n. Amyelinic nerve fibre termination; n.s. Neuron in spinal cord; 
s.R. Stellate cells connected with the odontoblasts; n.p. Nerve plexus of amyelinic 
fibrils. • 



158 THE DENTAL TISSUES 

filaments: there occur, however, many more nerve filaments 
than are in the dentinal canaliculi proper, which run between 
these, and in the same direction, in approximately the same 
direction, and in quite a different direction. The same direc- 
tion as that of the dentinal canaliculi is observed chiefly in the 
crown portion of the teeth, it is therefore more difficult to 
distinguish nerves there from other fibril constituents than it 
is, for instance, in the root portions." 

Inasmuch as this writer supposed that myelinic fibres 
entered the dentine in special tubes, and as these tubes are non- 
existant, his observations carry no weight whatever. 

10. Schafer 1 accepts Howard Mummery's conclusions but 
does not base his belief entirely on the microscopical appear- 
ances, but on clinical grounds also. But the sensitiveness of 
dentine can be explained in other ways than upon its supposed 
innervation. 

11. Howard Mummery 2 has devoted much patient labour 
to the elucidation of the nerve terminations. His conclusions 
may be summarised in his own words, as follow: 

(a). That, in actively growing teeth, there is a considerable 
supply of non-medullated or efferent fibres to the tooth pulp, 
which are derived from sympathetic ganglia and not concerned 
in any way with the sensitiveness of the dentine, their ultimate 
fibrils probably being distributed to the coats of the blood-vessels 
and the secreting cells of the pulp; whether any fibres of this 
system enter the dentinal tubes it seems impossible to 
determine; 

(P). That at the cornua of the tooth pulp, the bundles of 
medullated nerve fibers lose their medullary sheath and neuri- 
lemma, and the axis cylinder expands into a spreading mass 
of neurofibrils, which can be traced directly to the dentinal 
tubes, which they enter; 

(7). That in young, growing teeth, these fibres at the cornua 
are very abundant, and have a wavy course; they appear to 

1 "Essentials of Histology," 1016. 
2 "On the Distribution of the Nerves of the Dental Pulp," Philos. Trans. 
Roy. Society, 1912; "The Nerve Supply of the Dentine," Proc. Roy. Soc. Medicine, 
1012; "The Innervation of Dentine," Dental Cosmos, March, 1916, etc. 



THE DENTAL PULP 1 59 

consist of bundles of neurofibrils in many instances, and these 
vary much in diameter, the further divisions of these bundles 
probably taking place in the tubes of the dentine; 

(5). That at the lateral portions of the pulp, the neurofibrils 
passing from the main nerve trunks enter into an intricate 
plexus beneath the odontoblasts, and are again collected into 
larger strands of neurofibrils, which mostly pass directly into 



Fig. 134. — Diagram to show the method of termination of the amyelinic 
nerve fibres of the pulp in the dentine according to Howard Mummery, e. 
Enamel; d. Dentine; b. Limit of pulp tissue; o. Odontoblast; n. Amyelinic nerve; 
p.r. Plexus of Raschkow; m.p. Marginal plexus; t. Terminations in dentinal tubes 
beneath enamel. 

the dentinal tubes. They (the preparations) also demonstrate 
the different appearances of these strands of fibrils, some being 
large and showing bead-like enlargements at intervals, other 
finer fibres having a minutely dotted appearance; 

(e). That where the pulp is separated from the dentine, the 
nerve fibres seem to be pulled out from the pulp and from the 
dentinal tubes, and stretch across the interval, evidently under 
considerable tension; 

(f). That the nerve fibres enter the dentinal tubes in company 
with the dentinal fibril. 



c6o 



THE DENTAL TISSUES 



12. M. Pont in a contribution to the Trans, of the Illrd. 
International Dental Congress, Paris, 1900, on "La cataphorese 
en art dentaire et plus specialement dans le cas de dentine 




Pig. 135. — The cornu of the pulp of a fully formed human premolar. M. 
Myelinic nerve bundle dividing, inclosing the transverse section of blood- 
vessel; d. Dentine. Neurofibrils entering the tubules. Prepared and photo- 
graphed by J. Howard Mummery. 




Fig. 136. — The cornu of pulp of erupting human premolar, m. Myelinic nerve 
bundles dividing; N. Neurofibrils; D. Dentine; B. Blood-vessel. Prepared 
and photographed by J. Howard Mummery. 



hypersensible " says: "La description des odontoblastes rapelle 
absolument celle des neurones sensoriels peripheriques, et 
nous croyons que les odontoblasts sont des cellules nerveuses 



THE DENTAL PULP 



l6] 



dont les prolongements peripheriques constituent la voie 
centripete et les prolongements pulpaires la voie centrifuge." 
("Odontoblasts resemble peripheral sensory neurones, and we 
believe that they are cells of the nervous system, whose den- 
tinal processes constitute the centripetal poles and basal 
processes the centrifugal poles.") 




Fig. 137. — Ameylinic nerve fibres in the r dental pulp of man. 
From a drawing by the' 1 author. One fibre is seen approaching, on the 
left, its terminal arborisations. Stained by Dogiel's method. Magnified 
750 times. 



13. For many years, the present author has endeavoured to 
demonstrate the ultimate ramification of these nerves. His 
then views were set forth at some length in the Trans. Odonto. 
Soc. of Gt. Britain, November, 1893. Some of the arguments 
are reproduced in the Appendix. Since that communication 
appeared, he has not confined his investigations to the pulps 



:62 



THE DENTAL TISSUES 




Fig. 138. — Amyelinic nerve fibre in the dental pulp of man. Stained by 
Dogiel's method. Magnified 750 times, n.f. Nerve fibre bifurcating into two 
terminal branches; N. Nucleus of pulp cell. Photomicrograph by Douglas 
Gabell. 




Fig. 139. — Similar to Fig. 138. The beaded appearance is well shown. Photo- 
micrograph by Douglas Gabell. 



THE DENTAL PULP 



163 



Y'/'-C^}-. 



w 



K^ ' 



Fig. 140. — Longitudinal section of the'pulp of a human incisor tooth. Stained 
by Ford Robertson's modification of Heller's stain. Magnified 40 times. Shows 
the general arrangement of the myelinic nerve bundles. (From a section prepared 
by the late Storer Bennett.) 



164 



THE DENTAL TISSUES 



of the teeth of man alone, and has obtained abundant evidences 
in other vertebrates of the presence of amyelinic fibres at 
the periphery of the pulp. The photomicrograph Fig. 109 
represents a teased preparation of the myelinic fibres, which 
go to form a component part of the plexus of Raschkow. It 
was made thus: — A recent tooth, unaffected in any way by 




-The same as the preceding. Magnified 250 times. 



morbid influences, on being carefully split in the jaws of a 
vise, is found to have covering the inner surface of the dentine 
a moist, colourless, almost invisible film. Removal of this and 
staining with suitable reagents revealed a tangled mass of myel- 
inic nerve fibres. The staining reagents used were not espe- 
cially appropriate for amyelinic fibres. In other parts of the 
tissue numerous nerves of the latter class could be readily 
stained by using a }{q per cent, physiological solution of 
methylene blue, ''fixing" in picrate of ammonia, and mounting 
in glycerine. 



THE DENTAL PULP I 65 

As the result of his researches, the author has the strong con- 
viction that these fibres terminate in a basket-work of varicose 
fibres embracing and often closely attached to the cell walls of 
the individual odontoblasts. The sensory currents are traced, 
in this way, from the amelo-dentinal junction through the 
dentinal fibrils, odontoblasts, arborisations of amyelinic telo- 
dendria to the myelinic nerve fibres of the pulp. 



CHAPTER VIII 

THE ALVEOLO-DENTAL PERIOSTEUM 

Microscopical Elements: — (i) "Principal" fibres; (ii) Connective tissue 
fibres; (iii) Blood-vessels; (iv) Nerves; (v) Epithelial masses: (vi) 
Osteoblasts; (vii) Osteoclasts; (viii) Sharpey's fibres; (ix) Calco- 
spherite spherules. 

GENERAL CHARACTERISTICS 

Definition. — The thin connective tissue with extensive vas- 
cular and nervous systems which intervenes between the exter- 
nal surface of the cementum of teeth and the lamina dura of the 
bone of their alveolar sockets. Its synonymous terms are: — 
"Periodontal membrane," "root membrane," "dental perios- 
teum," or " alveolo-dental ligament." The expression "Perio- 
dontal membrane " is, for the sake of convenience, used here and 
throughout this work. 

Origin. — It is derived from the outer layers of the dental 
capsule. 

Distribution. — It exists in all teeth attached to the jaws by 
gomphosis articulation, viz.: those of man and most mammals, 
crocodiles, and a few uncommon fish. The teeth of the vast 
majority of fishes, and some reptiles, are fixed by either anky- 
losis, hinge, or membrane. In these the periodontal membrane 
is wanting. 

The gingival portion of the periosteum, according to Stohr, 1 
is called the "annular dentinal ligament," or the ligamentum 
circular e dentis. This is entirely incorrect, however: there are 
no tissues specially marked off from the others to form even a 
distant resemblance to a ligament. No constricting bands of 
strong connective tissue fibres exist at the cervical regions of 
the teeth. 

1 Stohr, "Text-book of Histology," Wurzburg; p. 112, 1914 
166 



THE ALVEOLO-DENTAL PERIOSTEUM 1 67 

Macroscopical Appearances. — A white dense membrane cover- 
ing over the roots of teeth, it varies in thickness in different 
individuals, in different teeth in the same mouth, and at varying 
periods of life. It is thickest in childhood and thinnest in 
senility. In measurement, in adult age, it ranges from 350^ 
to 500/x in width, and from 8 to 20 mm. in length. These are 
average statistics: in the localities where it dips into bays or 
recesses of the alveolar process, the width is proportionately 
increased. Its microscopical nature is best studied when the 
tissue is retained in situ, easily accomplished in sections pre- 
pared by fixing and hardening the soft part first in formalin, 
or Muller's fluid, and afterwards decalcifying with hydro- 
chloric or other acids, and finally cutting on an ether-freezing 
microtome. 

HISTOLOGY 

The several parts of the minute structure of the periodontal 
membrane may be described as follows: — (i) The fibrous ele- 
ments; (ii) Cells; (hi) Blood-vessels; (iv) Nerves; (v) Calco- 
spherite spherules. 

1. — The Fibres 

The fibrous elements are grouped into two separate and spe- 
cific divisions, which, however, are indistinguishable anatom- 
ically: — (A) The "principal" fibres, 1 and (B) The ordinary and 
less important connective tissue fibres. 

A 

The principal fibres of which the greater part of the mem- 
brane is composed are of the white connective tissue variety, no 
elastic fibres whatever being present (Black). Many are fas- 
ciculi of delicate wavy fibrils gathered together to form coarse, 
strong bands; but more commonly they run in loose bundles. At 
the neck of the teeth they pass immediately outward from the 
cementum, — the fibres generally lying fairly parallel to each 
other, — to be inserted into the fibrous mass of gum tissue. 

1 A term first suggested by Black in "Periosteum and Peridental Membrane," 
1887, to whom a great deal of our knowledge of the histology of this tissue is 
due. 



i68 



THE DENTAL TISSUES 



Nearer the radicular portion, the fibres merge into the connec- 
tive tissue fibres of the periosteum of the alveolus, from which 
they cannot be readily distinguished. In the apical region they 
are very irregular, or may be almost absent, this portion of the 
socket of the tooth being filled with small cells, and few fine 
fibres (the "indifferent tissue" of Black), with abundant room 
from the passage of blood-vessels and nerves. The apical region 




Fig. 142. — Transverse section of the periodontal membrane of man in situ. 
Prepared by the Author's process. Stained with Ehrlich's acid hasmatoxylene. 
Magnified 250 times. M. The root-membrane with its fibres and cells; b. Its 
blood-vessels; and e. Its epithelial gland-like bodies; d. Dentine; c. Structureless 
cementum; A. Bone of the alveolus; Oi. Osteoblasts on the wall of the alveolus; 
02. Osteoblasts on the surface of the cementum. 

may measure 0.5 mm. in depth. At the surface of the gum the 
fibres course in wavy lines directly outwards, i.e., at right angles 
to the long axis of the tooth, and then suddenly upwards to be 
inserted into the gum; at the neck of the tooth near the alveolar 
margin they are inclined root-ward, and are inserted into the 
bone or periosteum. At the mid-distance — otherwise the 
alveolar portion of the membrane, — they run squarely across; 
but near the apex of the root, they assume a crownward direc- 
tion. At the apical region itself they radiate from the cemen- 
tum to the bone. 



THE ALVEOLO-DENTAL PERIOSTEUM 



169 



The fibres which arise from the cementum are finer than those 
inserted into the lamina dura, and are continuous with Sharpey's 
fibres of the cementum; and the large ones, as a rule, break up 
into delicate bundles of fibrils. 

They all pursue a rather sinuous course, being deviated 
from straight lines by the presence of the vascular and nervous 
zones in the central portions of the membrane. 




Fig. 143. — The fibres of the periodontal membrane, d. Dentine; c. Cementum; 
f. Fibres. Preparation and photomicrograph by Dr. H. Box, Royal College of 
Dental Surgeons, Toronto. 



B 



The ordinary fibres are found among the foregoing. They are 
the common type of connective tissue fibres with nuclei and 
tissue corpuscles. They are arranged diagonally to the prin- 
cipal fibres, and are usually difficult to distinguish, on account 
of their feeble staining properties. 

2. The Cells 

The cellular elements are of several varieties. 
(a) The lamellar connective tissue corpuscles are spindle- 
shaped, nucleated, ramified, and very prominent. They are 



170 



THE DENTAL TISSUES 




Fig. 144. — A small area of a transverse section of the root of a tooth, and a 
portion of the periodontal membrane, showing glands. D, Dentine; CM. 
Cementum; g.l. and G.iA Tubular glands (?) winding among the fibres of the 
membrane. {Photomicrograph by G. V. Black.) 



THE ALVEOLO-DENTAL PERIOSTEUM 



171 




^ET 



•*h 



! 




Fig. 145. — Epithelial bodies in the periodontal membrane, cm. Cementum; 
C.B. Osteoblasts lying between the fibres of the membrane close to the cementum; 
G.L. Epithelial cells with nuclei; c.c. Connective tissue cells. (Photomicrograph 
by G. V. Black.) 



172 



THE DENTAL TISSUES 



called "fibroblasts" by Black. They are freely distributed to 
all parts of the membrane. 

These cells, or corpuscles, differ in no essential particular from 




Fig. 146. — Showing gland-like epithelial bodies lying between the large 
white fibres of the root membrane, d. Dentine; cm. Cementum; c.b. Osteo- 
blasts; GLi; GL2, Glands (?); F. Large white connective tissue fibres. (Photomicro- 
graph by G. V. Black.) 

the ordinary cells or corpuscles of connective tissues generally. 
Thus, they are nearly always of the flattened or lamellar pattern. 
They are frequently affixed to the surfaces of the peripheral 
fibres; may extend between several fasciculi; and are most com- 



THE ALVEOLO-DENTAL PERIOSTEUM 1 73 

monly joined by means of branching processes, which in this 
manner form delicate reticula throughout the tissue between the 
principal fibres. 

They are composed of clear granular protoplasm, and their 
nuclei are oval or fusiform in shape. They may be well shown 
by staining the membrane in situ with chloride of gold imme- 
diately after extraction, stripping from the surface of the 
cementum, and teasing-out pieces thus removed in a plane 
parallel to the periphery of the root. 

((3) Osteoblasts are flattened, cubical, or irregularly shaped 
nucleated cells applied intimately to the external surface of 
cementum and bone. This irregularity in shape, in the former 
situation, according to Noyes ("American Text Book of Opera- 
tive Dentistry, p. 144, 1901), is caused by these cells "fitting 
around the attached fibres of the membrane, so as to cover the 
entire surface of the membrane between the fibres." They are 
called " cementoblasts " by Black, Noyes and others; but no 
points of morphological difference can differentiate them from 
those ordinary osteoblasts which are found in the inner layer of 
the periosteum of the alveolar bone. This being the case, 
it is advisable to delete the word "cementoblast" from dental 
terminology. 

(7) Osteoclasts, or myeloplaxes, are multi-nucleated giant 
cells, oval in shape, being found where absorption of either bone 
or cementum is in progress. They measure 30^ in diameter, 
and are most frequently discovered in the bay-like recesses 
(the foveolas of Howship) on the periphery of these hard tissues. 
In the periodontal membrane they lie in close contact with 
the surface, which they are about to absorb, and thus, while 
intervening in the interfibrous spaces, destroy or cut off the 
ends of the principal fibres, when they, as Sharpey's perforating 
fibres, are built into the bone or cementum. 

(<5) Epithelial cellular bodies or "rests" are not infrequently 
observed in the inner portion of the periodontal membrane. 
They appear near the cementum, just outside the layer of osteo- 
blasts, and are seen exceedingly well in ' horizontal sections. 
Very pronounced are they in the root membranes of the teeth 
of the sheep and pig, less so in man, except in the teeth of 



174 THE DENTAL TISSUES 

the young. Attention was originally attracted to these masses 
by Malassez 1 in 1885; and Black described and figured them 
in •"Periosteum and Peridental Membrane." 1887; but in 
ascribing to them the role of lymphatics, he was probably 
incorrect, as no true lumina have ever been discovered, and 
their connection, if any. with the hypothetical lymphatic 
system has never been traced. This worker has. however, 
modified his views on their functions and character in his 
latest addition to the literature of the subject (The Dental 
Cosmos, p. 101. 1899). 

Most probably, whatever be their functions, they take their 
origin from scattered, unabsorbed. or unatrophied remnants 
of the epithelial sheath of Hertwig. as was first pointed out 
by von Brunn, 2 or from vestigial remains of the tooth-band, 
which have persisted after disappearance of that structure. 

Under magnifications of 250 diameters, their histological 
characteristics can be easily discerned in suitably stained cases. 3 

Situated between the principal fibres, and running generally 
in an outward direction, they assume the form of cords or 
tube-like collections of epithelial cells, each of which contains 
in the centre a large oval nucleus. Surrounding each "rest" 
is. apparently, a very delicate basement membrane. Cut 
obliquely, there is some trace of what might be a lumen: but 
the glandular nature — or otherwise — of these bodies as described 
by Black requires more investigation and confirmation before 
dogmatic statements as to their real character can be expressed. 

Regarding the so-called "gingival gland." Black writes as 
follows: ■"This is a small lobulated mass of connective tissue 
cells lying close to the attachment of the gum to the tooth at 
the gingival line. It is mostly included within the prolongations 
of the epithelium of the gingival trough, or that which covers the 
portion of the free margin of the gum lying next to the neck of 
the tooth. It has a strong glandular appearance. Its cellular 
elements are not epithelial, but are round connective tissue cells. 

1 "On the Existence of Masses of Epithelium round the Roots of Adult 
Teeth, in a Normal State." Journal of the Brit. Dent. Association. 
- Archiv. fiir Mikroskop. Anatomic, 1887. 
3 Haematoxylene is a useful reagent. 



THE ALYEOLO-DEXTAL PERIOSTEUM 



175 



D|Ts 




Fig. 147. — Supposed duct of glands of the root membrane, starting from a 
group of glands not shown in the field. CM. Cementum; d.Ti. d.tj, d.Tj. Duct; 
F. Fibres of the membrane; b.l. Blood-vessels. (Photomicrograph by G. V. Black.) 



176 



THE DENTAL TISSUES 




Fig. 148. — The so-called "gingival gland." s.g. s.g. Gland; cm. Cementum 
parted from the dentine; n.m. Nasmyth's membrane separated from the enamel 
by the acid used in decalcification; e.p.l. Epithelial column dividing the gland 
from the surrounding tissues; except at its base; e. Epithelial cells; e.p. Epi- 
thelium of outer portion of free margin of the gum; g.l. Glands of root membrane; 
d.t. Duct leading from glands towards the gingivus; d.Tl>. Small loop of second 
duct; f. Fibrous tissue of the gum. {Photomicrograph by G. V. Black.) 



THE ALVEOLO-DENTAL PERIOSTEUM 1 77 

These are in lobules, divided in part by delicate hyaline mem- 
branes, which often appear double in sections, occasionally 
giving the appearance of ducts. But close studies of them 
indicate rather that they are duplicatures of the membrane 
envelope. In part, the lobules are divided by epithelial bands 
from the prolongations of the epithelium of the gingivae. A 
strong epithelial band from the gingival epithelium encircles the 
whole mass and parts it from the neighbouring tissues except 
at its base. In cross-sections this epithelial band is seen to be a 
continuous sheet without break. Though definitely lobulated, 
this body does not seem to possess the character of a gland, 
and I should not suppose from an examination of this tissue 
that it had a glandular function. It encircles but a portion 
of the neck of the tooth, usually only the approximal portion, 
thinning away towards the buccal or lingual, so that in many 
of the lengthwise sections it may be very small or does not 
appear at all." 

3. The Vascular System 

This lies in the central zone of the tissue and is fairly abun- 
dant. Arterial branches having a common origin with those of 
the pulp pass towards the crown from the apical region. Run- 
ning thence, they branch, divide, and subdivide and are freely 
distributed through the body of the membrane, meeting and 
inosculating with the vessels of the gum and periosteum, and 
even occasionally of the Haversian systems of the alveolar 
bone. 

The capillary network is scanty, the blood supply of the 
membrane being chiefly arterial and venous. Of the former 
the largest vessels, in horizontal section, may measure 0.05 
mm. to 0.1 mm. in diameter. 

The veins accompany the arteries. 

4. The Nervous System 

The exact manner of the distribution and nature of the ulti- 
mate terminations or ramifications or anastomoses of the 
nervous supply of the root membrane is unknown : it is a branch 
of Dental Histology, which so far has been practically ignored. 



178 THE DENTAL TISSUES 

According to Noyes, however, "six or eight myelinic fibres 
enter the apical region in company with the blood-vessels, 
and they receive other trunks through the walls of the alveo- 
lus and over the border of the alveolar process" {Op. cit. p. 155). 

5. Calcospherite Spherules 

Tiny, almost structureless, rounded masses of calcoglobulin, 
called calcospherite spherules, may occasionally be found near 
the epithelial bodies. They are more constant in inflammatory 
conditions of the membrane (q.v.). 







Fraak J. butler del 

Two Phases of Dental Histogenesis m Mammalia. 



DESCRIPTION OF PLATE II 

Fig. A. — Sagittal section through the mandible of a pup at birth. Fixed, 
hardened and decalcified. Cut on an ether-freezing microtome. 

i, Dentine papilla; 2, Dentine; 3, Enamel; 4, Enamel organ; 5, Part of dental 
capsule; 6, Alveolus of jaw forming the socket of the tooth; 7, Mandibular canal. 
A. Ameloblasts; b. Stratum intermedium; C. Stellate reticulum; D. External epithe- 
lium; e. Mandibular artery; f. Mandibular veins; g. Mandibular nerve. 

Fig. B. — Lateral half of coronal section through mandible of a foetal rat. 
Prepared similarly to preceding Figure. 

1, Dermal structures on under surface of jaw; 2, Muscle fibres; 3, Muscle fibres 
of tongue; 4, Lingual papillae; 5, Salivary gland; 6, Nerve bundles; 8, Root of 
incisor tooth cut through; 9, Molar tooth; 10, Muscle fibres, a. Hairs cut trans- 
versely; B. Hairs cut obliquely; c. Enamel organ of incisor tooth; D. Tooth-band; 
E. Enamel organ; f. Enamel; G. Dentine; H. Odontoblasts. 



PART II 

THE ORAL TISSUES 



CHAPTER IX 
THE ORAL CAVITY AND ITS ACCESSORIES 

Microscopical Elements of the: (i) Lips and cheeks; (ii) Tongue; (iii) 
Salivary glands; (iv) Hard and soft palate; (v) Palatine tonsils. 

THE LIPS AND CHEEKS 

These consist for the most part of muscular tissue, which is 
freely supplied with blood-vessels and nerves. Loose areolar 
tissue, fat lobules, and great quantities of minute glands make 
up the rest of their substance. Externally they are protected 
by skin, internally by mucous membrane. This is studded 
everywhere with myriads of vascular papilla? of microscopic 
size. In many papilla? nerve-end-bulbs are found. 

"Labial" glands (small racemose bodies) have the free ter- 
minations of their excretory ducts directed to the inner surface 
of the lips, "buccal" and "molar" glands to that of the cheek, 
while small sebaceous glands occur in the outer part of the red 
border of the lips. 

The mucous membrane of the mouth generally is lined with 
epithelium of the stratified squamous variety, many "spiny" 
cells lying in the deeper layers. 

THE TONGUE 

The tongue is a large soft organ, flattened from above down- 
wards, situated in the floor of the mouth. 

It consists mainly of muscles, extrinsic and intrinsic, the 
latter being those placed entirely in its substance. The fibres — 
striated and voluntary — exhibiting the usual features of 
striped muscular tissue generally, run in various directions, 



182 



THE ORAL TISSUES 



so that in any and every section, some are cut longitudinally, 
some vertically, others transversely, thus forming particularly 
attractive preparations for the microscope. 

Greater interest than that of the histology of the muscles, 




Fig. 149. — Coronal section of the tongue of a dog. Prepared by hardening 
in alcohol. Stained with haematoxylene and eosine. Magnified 12 times, 
s. Superior surface or dorsum of tongue; c. The epithelium of the filiform papillae; 
B. Blood-vessels injected with carmine; 1. Inferior surface of tongue. 



however, attaches to the mucous membrane and its abundant 
supply of eminences or papillae of varying size and shape. 

The anterior two-thirds of the dorsum presents on its sur- 
face, tip, and sides, where the mucous membrane is thin and 
closely adherent to the muscular layer beneath, enormous 
numbers of papilla? known as "filiform," "fungiform," and 



THE TONGUE 



"circumvallate." All are macroscopically visible, but micro- 
scopically of considerable interest. 



HISTOLOGY 



Each papilla is covered, like the rest of the oral mucous 
membrane, with multitudes of secondary papilla? closely em- 
braced by the epithehiirn. Each contains a capillary loop, and 
plexus ol nerves. 




~\J 



Fig. 150. — Vertical section of tongue of man. Prepared in the usual way. 
Stained with haematoxylene. Magnified 70 times, f. Conical papilla; s. 
Secondary papilla; h. Epithelium of laminated structure between the papillae, 
and extended into ciliform processes over it. l. Tunica propria; v. Muscle 
fibres cut vertically; T. Muscle fibres cut transversely. 

As already stated, the papillae are of three kinds: — 
1. The conical papilla abound all over the dorsum, but are 
absent from the base of the tongue. In shape they are tiny 
elevations with tapering or cone-shaped extremities. They 
are the smallest of the three varieties, measuring, in man, to 
the base of the mucous membrane, 0.9 mm. to 1.0 mm. in length. 
Their secondary papillae are peculiar and unique in containing 



184 THE ORAL TISSUES 

great quantities of elastic fibres, and being clothed by special 
epithelium of a cornified nature, which "forms a separate horny 
process over each secondary papilla, greater in length than the 
papilla which it covers" (Schafer). 

When a bundle of these thread-like projections exists over 
the conical papillae (which are often quite devoid of them), the 
term "filiform" is employed to designate the character of the 
papillae. They are easily found on the surface of the tongues 
of cats and other carnivorous animals. 




Fig. 151. — Fungiform papillae with gustatory cells of tongue of rabbit. Stained 
with carmine. Magnified 30 times. 

2. The fungus-shaped elevations which beset the middle 
and fore part of the tongue are called fungiform papillce. In 
the recent state they are of a bright red colour. Possessing 
blunt rounded extremities, they are attached by narrow 
foundations. 

3. Most interesting of all, are the circumvallate papilla, so 
called from their environment. Each is placed in a poculiform 
depression of mucous membrane, and has a cone-shaped ap- 
pearance, surrounded as it is by a trench or fossa, on the 
outer free margin of which is a slight elevation of mucous 



THE TONGUE 



t»S 



membrane. This, completely circling the papilla, is the 

vallum, which is comparable to a rampart. Hence the name. 

These papillae are very few in number, sometimes not more 

than a dozen existing on one tongue. They are located on 




Fig. 152. — Circumvallate papilla of the tongue of man. Prepared in the 
usual way. Stained with haematoxylene, and counter-stained with eosine. 
Magnified 30 times, p. Circumvallate papilla (its epithelium); f. Fossa; v. 
Vallum; d. Duct of gland opening into base of fossa; c. Corium of papilla. 



the posterior third of the organ, arranged in two rows, which 
meet together at a point, like the arms of the letter V. In width 
they may measure as much as 2.5 mm.; width inclusive of the 
vallum on either side 4.5 mm. In addition to the vascular 
and nervous supply of the corium, the stratified epithelium 
which is extremely thick, contains in it several "taste buds or 



i86 



THE ORAL TISSUES 



goblets," both on the sides of the papilla itself and in the mucous 
membrane of the fossa. At the base of the fossa, which may 
measure 1.25 mm. in depth, the openings of the ducts of one 
or more glands can be seen. 

"Taste-buds" are oval in outline, and consist of a collection 
of narrow and fusiform gustatory cells, all enclosed by a single 




Fig. 153. — The gustatory cells in a fungiform papilla of the section photo- 
graphed in Fig. 151. Magnified 300 times, g. Goblet or gustatory cells. 



layer of broader fusiform cells, the encasing cells. A slight 
depression in the lingual epithelium over the goblet has at its 
base, a group of fine trichinous processes, which are the ter- 
minations of these gustatory cells. 

The base of the tongue contains many lymph nodes scattered 
in diffuse lymphoid tissue in the tunica propria, (collectively 
named the "lingual tonsil"), and numerous mucous glands. 
The latter are large and broad, their dimensions, in man, being 
1.4 mm. in width, and even 3.0 mm. in length. They possess 
the usual histological features of mucous glands generally 
(Fig. 162). 



THE SALIVARY GLANDS 1 87 

THE SALIVARY GLANDS 

The parotid, sublingual, and submaxillary glands secrete 
saliva. 

In man, the former is composed of acini of serous cells; 
the sublingual of mucous acini, and the latter of both, though 
the serous acini preponderate. According to its secretion, 
so do the histological elements of each gland differ. 

HISTOLOGY 

They are compound racemose glands (Fig. 158), consisting 
of an aggregation of lobules, each of which has a duct which, 
after branching, terminates, on the one hand in fine small 
branches into which the acini of the glands open, and on the 
other, in larger ducts which ultimately end by a free orifice 
on the surface of the mouth. Many blood-vessels ramify in 
a small amount of loose connective tissue, which forms the 
investment for the lobules, and for the gland itself. In the 
last situation, the capsule contains ordinary flattened cells, 
a few granular plasma-cells, lymph corpuscles, and occasionally 
a little adipose tissue. 

Duels 

Histologists arbitrarily divide the ducts into an intralobular 
part and an intercalary part. The intralobular portions, larger 
than the rest, and near the free opening of the duct, are lined 
with epithelium of which the cells have the following charac- 
teristics: — They are large, columnar or conical in shape, with 
their truncated extremity directed towards the lumen: they 
have a centrally placed spherical nucleus: they are granular 
at their inner and finely striated at their outer extremities 
(see diagram, Fig. 159). 

The fibrillated markings are well seen in the submaxillary 
gland. 

The large ducts are covered with a coating of fibrous and 
elastic tissue, intermingled with a few small involuntary muscular 
fibres. 



THE ORAL TISSUES 



The intercalary portions, shorter and narrower than the pre- 
ceding, extend to the acini, and are lined with clear flattened 
cells, possessing elongated nuclei, at their most distal part. 
As they approach the intralobular ducts, their lumina are lined 




Fig. IS-!-- — Vertical section through base of the tongue of man. Prepared 
by hardening in 3 per cent, nitric acid, and subsequently staining with methylene- 
blue. Magnified 25 times, g. Mucous gland; d. Duct of gland opening on to 
the surface; p. Conical papilla; m. Muscle fibres. 

with cubical cells with small nuclei (see Figs. 159 and 160). 
Acini 

The acini constitute the secreting part of the glands, and 
are of two kinds: (A) mucous, and (B) serous. 



THE SALIVARY GLANDS 1 89 

A 

Mucous Acini 

Bounded by a delicate reticulated basement membrane, 
each acinus is lined by a single layer of true secreting cells. 
These vary according to their activity or passivity. 

In the latter condition they are large, clear, granular, and 
spheroidal in shape, and nearly fill the whole of the acini. 
They take stains very indifferently. Each nucleus, somewhat 




Fig. 155. — Transverse section of salivary gland of cat, stained with picric 
acid, blood-vessels injected with carmine. To show its abundant vascular 
supply. Magnified 30 times. 

flattened, is placed near the basement membrane. The trans- 
parent appearance is due to the presence of mucin or mucigen. 

In addition, there are also found certain marginal cells, the 
crescents of Gianuzzi (the demilunes of Heidenhain of some 
authors). They have semilunar outlines, are small, very 
granular, and stain deeply with the usual dyes. 

In an active state, as the result of stimulation, the cells stain 
readily, become rather smaller and more granular, and the 
nuclei, now no longer compressed, occupy the central parts of 
the cells (see Figs. 161 and 162). 



190 THE ORAL TISSUES 

B 

Serous Acini 

At rest, these cells, when properly prepared and stained, 
are granular, with their nuclei in their centres completely 




Fig. 156. — Submaxillary salivary gland of : 
way Stained with Ehrlich's acid hasmatoxylene 



several lobules, s.s. Serous; m.m. Mucous; 
between the lobules. 



a. Prepared in the usual 
Magnified 20 times. Shows 
Blood-vessel; c. Connective tissue 



obscured by the albuminous material in their protoplasm. 
The lumen similarly to that of a mucous acinus is frequently 
totally occluded. 

During a period of prolonged activity, the cells appear to 



THE SALIVARY GLANDS 



191 



be shrunken, a few granules have collected in their inner 
aspects, the nuclei are clearly revealed and easily recognised, 
and the lumen is large and patent. These changes are depicted 
in the accompanying diagrams (Figs. 163 and 164). 




Fig. 157. — Diagram of 
a racemose gland. 





. — Intralobular Fig. 159. — Mucous 
duct. tercalary duct. 




Fig. 160. — Serous 
tercalary duct. 




Fig. 161. — Acinus of 
a mucous gland during 
a period of passivity. 




Fig. 162. — Acinus of 
a mucous gland during 
a period of activity. 





Fig. 163. — Acinus of 
serous gland during 
period of passivity. 



Fig. 164. — Acinus of 
a serous gland during a 
period of activity. 



HARD AND SOFT PALATE 



The histology of the osseous framework, and fibrous covering 
of the roof of the mouth requires but a brief survey, a descrip- 
tion of its bony structure appearing in the following Chapter. 



HISTOLOGY 



The bone is covered with a thin layer of periosteum and 
mucous membrane. Of the former nothing need further be 
said, its character being similar to that of the periosteum of 
bones generally; the latter, however, thrown into folds {palatal 



192 



THE ORAL TISSUES 



ruga) exhibits the same characteristics as in other parts of the 
mouth, except that in these ridges, as well as in the papilla 
palatina or incisive pad, the cells are larger, coarser, and more 
multiplied than elsewhere. 

The vascular and nervous supplies are scanty, as is also the 
number of mucous glands. Adipose tissue is present to a limited 
extent. 



«T 




v ■■•■■-, 






Fig. 165. — Vertical section of the hard palate. Stained with hamatoxylene 
and eosine. Magnified 200 times, o.e. Oral epithelium, with surface projecting 
as ruga?; s.p. Simple papilla; c.P. Compound papilla; B.v. Blood-vessel; b. Surface 
of palate bone; p. Periosteum. 

The soft palate consists of voluntary muscular fibres, and a 
great number of glands all clothed with mucous membrane, 
which is covered on the anterior surface with stratified squa- 
mous epithelium, and on the posterior surface with ciliated col- 
umnar cells. It measures approximately 10 mm. in thickness. 

The uvula consists chiefly of voluntary muscle fibres and 
compound racemose glands, which abound in great numbers 
on the anterior surface of the soft palate where they form an 
almost complete layer under the squamous stratified epithelium. 

THE FAUCIAL OR PALATINE TONSILS 

The tonsils are soft, very vascular bodies placed between 
the anterior and posterior palatine arches or pillars of the 
fauces. 



THE TONSILS 1 93 

HISTOLOGY 

They are composed of lymphoid tissue enclosed in a fibro- 
elastic capsule. Dense masses of lymphoid cells are collected 
here and there, and form the lymphoid follicles of the tonsil. 
The latter are large oval or round bodies having a breadth, 
in man, of 1.5 mm. and a length of 3.25 mm. 









' r i^TV ^h 




v S 






Sim 








OE 












AT 








••' 








MG 


ijyptJEv^s 


*/£"'„ 









Fig. 166. — Vertical section of oral surface of the soft palate. Stained with 
haematoxylene and eosine. Magnified 200 times, o.e. Oral epithelium; m. 
Voluntary muscle fibres; m.g. Mucous gland; a.t. Adipose tissue. 

The framework of the follicles is a delicate stroma of fine 
retiform connective tissue, similar to the white fibres of areolar 
tissue. Hence it contains no nucleated cells as such, but 
trabecular of fibrous tissue surrounded by an open network 
of fibres more or less densely aggregated. 

The cells contained in these are lymphoid cells, which re- 
semble lymphocytes. They differ, however, in the facts that 
they have less cytoplasm, and a relatively larger nucleus. 

Stratified squamous epithelium extends over the exposed 
part of the tonsil. Opening on the free surface of the organ 
are numerous crypts or clefts into which the epithelium dips, 
13 



194 



THE ORAL TISSUES 



being continuous all over except at the tiny orifices of a few 
mucous glands, the ducts of whose acini open on to the surface 
of the crypts. 




Fig. 167. — Vertical section of tonsil of man. Prepared by fixing and harden- 
ing. Stained with haematoxylene; counter-stained with eosine. Magnified 60 
times, l.f. Lymphoid follicle; c. Crypt of tonsil; d.c. Lymph cells passing through 
the epithelium of crypt; G. Mucous gland; d. Duct of same, opening into the base 
of crypt. 

Lymphoid cells pass through this epithelial layer of cells 
from the follicles; become free and detached on the surface; 
and mixing with the saliva, appear as the so-called "salivary 
corpuscles." 



CHAPTER X 

THE HISTOLOGY OF THE MAXILLARY AND 
MANDIBULAR BONES 

Microscopical Elements in: (i) Bone of Canine fossa; (ii) Interdental 
septa; (iii) Hard Palate; (iv) Wall of Antrum; (v) Angle of Mandible; 
and (vi) Alveolar process. 

The hitherto published descriptions of the minute structure 
of the osseous framework of the lower face and jaw,- — such 
structures as are, in a word, in direct anatomical relation- 
ship and continuity with the teeth of man, — have necessarily 
been given only very infrequently; but in addition to this, 
the descriptions which have appeared in text-books and jour- 
nals have taken for granted that the histology of these par- 
ticular bones corresponds with that of tabular and irregular 
bones in general. 

To make this contribution complete, a few forewords are 
necessary and advisable. 

GENERAL CHARACTERISTICS 

Origin. — Each maxilla is probably developed from one centre 
of ossification as a membranous bone, at a spot which marks the 
site of the canine tooth germ, external to the cartilaginous 
nasal capsule. Each premaxilla is developed from one centre of 
ossification. Each half of the mandible, according to Low 
(Proc. Anat. Soc. of Great Britain andlreland, 1905), is developed 
from one — the dentary — centre in membrane. Meckel's car- 
tilage does not form bone, except that it becomes ossified and 
incorporated with the mandible just below the lingual side of 
the sites of the sockets of the first and second incisors. 

Distribution. — Both forms of bone, known as compact 
(smooth, dense, and ivory-like) and cancellated or spongy 



196 THE ORAL TISSUES 

(rough, open, and soft) are met with in the jaws. The former 
is found covering each surface both of maxillae and mandible, 
the latter constituting the intervening tissue, which in the 
case of the lower jaw is similar to the diploe of the cranial 
bones. The compact forms a somewhat thicker shell or 
crust on the external and internal surfaces of the mandible 
than on any portion of the maxillae. Compared with the bone 
of the sockets of the teeth of the mammalia generally — par- 
ticularly those of the hyena — that of man is a degenerate 
structure, on account of the fact that its blood supply is feeble 
and inadequate, it serves for the attachment of no muscles except 
a few fibres of the buccinator, and it is therefore almost func- 
tionless, and rapidly undergoes at its gingival margins physio- 
logical absorption or atrophy. (See Appendix.) 

HISTOLOGY 

Before considering the special histology of the bones of the 
jaws, a brief description of the structure of osseous tissue 
generally must be given. 

Bone of the jaw, as bone elsewhere, consists of a calcified 
fibrous ground-substance or matrix arranged as lamellae around 
spaces of varying shape, size, and contents which everywhere 
penetrate it in all directions. Of these the following are to be 
noted: (a) Haversian systems, (b) lamellae, (c) periosteum, 
and (b) Sharpey's fibres. 

(a) An Haversian system consists of an Haversian canal, 
several lamellae, with numerous lacunae and canaliculi. 

Interpenetrating everywhere are short longitudinal pas- 
sages or tubes which in cross-section appear as rounded or 
oval apertures, and, longitudinally cut, like short, straight, 
or slightly curved spaces of fairly regular diameter through- 
out. These are the Haversian canals. The largest may meas- 
ure iooju in width, the smallest 20^, the average size being about 
50/i. 

They are surrounded by lamellae, — thin bands of bony 
material arranged concentrically round each canal. Dark 
and light alternate, the difference in the refraction being due 
to the fact that the opaque lines are occasioned by the calcified 



THE MAXILLARY AND MANDIBULAR BONES 197 

fibrils running longitudinally, and the clear zones by their 
running transversely. In consequence, the ends only of the 
fibrils are cut across (see Fig. 176). 

Situated between these lamellae are bone-lacunas with their 
canaliculi. The first are flattened branched spaces, which 
may measure 14/i in their greatest diameter. In dried speci- 
mens they look like myriads of tiny, dark, fusiform specks 
arranged with fairly uniform regularity between the lamellae, 
and fully connected with each other and with the Haversian 
canals by means of many long, narrow tubes or canaliculi which 
cross the lamellae. Each cavity is filled with or contains a bone- 
cell with a large oval nucleus, as first described by Virchow. 
These are homologous with those of ordinary connective 
tissue. The wall of each lacuna is formed of some substance 
which resists the action of decalcifying reagents in a similar 
manner to the sheaths of Neumann in dentine. 

The contents of an Haversian canal, in the recent state, 
comprise several capillaries, small arteries and veins, a bundle 
of nerve-fibrils, and a few lymphatic vessels, all imbedded in 
fine connective tissue, which is surrounded externally by a 
tough lining membrane possessing properties identical with 
that which obtains also in the membranous lining of the walls 
of the lacunae. 

(b) In addition to the concentric lamellae, others arranged 
parallel to the surface of the bone, are called "circumferential" 
or "peripheric;" while a third set, when found between the 
Haversian systems, are commonly spoken of as "interstitial." 
Their structures differ in no particular from the concentric 
lamellae. 

(c) The periosteum can be well studied microscopically in 
sections where the hard and soft parts have been retained 
in situ. Bony periosteum consists of two layers, an outer, 
made up chiefly of white fibrous tissue, and an inner, of the 
same with few yellow elastic tissue fibres and capillaries in 
addition. In developing bone, osteoblasts — small, cubical, nu- 
cleated cells — are also present in this inner osteogenetic layer. 

(d) Sharpey's perforating fibres are noticed in thin strips 
of decalcified bone near the surface. They thus run in from 



190 THE ORAL TISSUES 

the deep surface of the periosteum and pierce the peripheric 
lamellae in a perpendicular or oblique direction. The fibrous 
bundles are of varying lengths, and taper gradually to their free 
extremities. They are fasciculi of fibrils, probably of white 
fibrous tissue; though it has recently been shown that many 
are perhaps elastic fibrils. When they do not become calcified 
they shrink and leave tubes in the channels in the dry bone. 
Sharpey also first demonstrated the presence of decussating 
transparent fibrils which constitute the main part of the lamellae 
(see Fig. 176). In this way, in bone, Sharpey's discoveries 
include both perforating and decussating fibres, the former 
being bundles of fibrils, the latter an exceedingly delicate 
network of fibres. In dental histology Sharpey's fibres are the 
fibres which run from the periodontal membrane into the 
cementum; while his homologous fibres in dentine matrix 
were originally seen and described by von Ebner 1 and later by 
J. Howard Mummery. 2 

Turning now to the minute structure of several typical 
portions of the bones of the jaws, it will suffice to point out 
their distinguishing features. 

(i) Bone of Canine Fossa 

In vertical lateral sections of the bone of a young subject 
(age ten and a half years) , it is found that the greater part of 
the tissue is composed of a dense osseous substance, but very 
scantily supplied with Haversian systems. Large areas of 
bone are quite devoid of either lamellae, lacunas, or canaliculi 
(Fig. 168). The matrix is distinctly coarsely granular (see 
Fig. 169), and has in it an indefinite number of short canals, 
the majority of which do not always communicate with lacunae. 
These tiny tubular spaces, probably in the recent state, contain 
connective tissue fibrils, as they are too minute for the con- 
veyance of blood-cells or even lymph. They are most marked 
and most numerous in the neighbourhood of the lacunae, the 
canaliculi of which they somewhat resemble. Varying in 

1 "Handbuch der Zahnheilkunde," Vienna, 1890-91. 
2 Philos. Trans. Royal Society of London, 1891. 



THE MAXILLARY AND MANDIBULAR BONES 



190 




Fig. 168. — Vertical section of the bone of the canine fossa; from a dried speci- 
men. Magnified 45 times. Unstained. Shows its general histological features. 
The dark masses are crowds of lacuna;, the lighter portions the ground substance. 




Fig. 169. — Granularity of the osseous matrix of the floor of the canine fossa. 
Magnified 750 times. Unstained. 



THE ORAL TISSUES 




Fig. i 70. — Abrachiate lacunae from a dried specimen of the floor of the canine 
fossa. Magnified 750 times. Unstained. In the matrix a few short canals 
can be seen. 




Fig. 171. — Vertical section of the bony septum between two maxillary premolars. 
Magnified 40 times. Unstained. 



THE MAXILLARY AND MANDIBULAR BONES 201 

length, their diameter measures about i/x- Several are shown 
in the photomicrograph Fig. 169. 

The Haversian lamellae, when they do occur, are but feebly 
marked. They do not present the usual microscopical 
characteristics of other bones, being very irregularly disposed 
in position and in shape, size, and constituents. 

The lacunas are massed together without order or regu- 
larity. Many are spherical in shape and absolutely unlike 




Fig. 172. — Radiograph of left side of normal jaws of man aged forty-five 
years, showing at l.d. the lamina' ditrtr. A certain amount of absorption of the 
terminal margins ot the alveolar processes has, here and there, occurred. 

those of well-constructed compact bone, the majority being 
provided with short coarse offshoots, though great numbers 
are quite abrachiate. This last fact is of great interest, and 
probably has also some pathological significance. These 
lacunae, as is well shown in Fig. 171, do not possess, and they 
probably never did possess, canaliculi; their outlines are 
sharply defined rounded or oval contours, and under low 
magnifications rather simulate dentinal tubes cut transversely. 



202 THE ORAL TISSUES 

In addition to the granular matrix, the substance of the 
bone, thin though it is, contains numbers of broad channels 
of great length, which may perhaps, during life, act as venous 
carriers of the blood or give passage to lymphatic vessels. 
Possessing no histological or physiological interest, they occur 
sufficiently commonly in this situation to warrant merely a 
passing reference. 




Fig. 173. — Radiograph of right side of jaws of man aged forty-five years, showing 
at l.d. the lamina dura. 



(ii) The Interdental Septa 

These are composed of cancellated bone the lattice-like 
character of which differs in no material degree from spongy 
bone elsewhere. The lamellae are arranged, as a rule, in 
lines parallel to the edges of the large openings in the bone. 
The lacunae are very numerous; a few are abrachiate, but by 
far the greater number possess canaliculi (Fig. 171). 

Thin sheets of compact bone exist normally immediately 
outside the periodontal membranes of the teeth. These are 



THE MAXILLARY AND MANDIBULAR BONES 203 

called Lamina dura,. Good radiographs show them in a marked 
degree, see Figs. 172 and 173. 

In the recent state, the large open spaces in the bone are 
filled with quantities of red medullary tissue, viz. — delicate 
branching, retiform tissue supporting the marrow cells of 
Kolliker, and small coloured nucleated cells many of which 
undergo sub-division by mitosis. 




Fig. 174. — Sagittal section of the substance of the hard palate. Magnified 
250 times. Unstained. The photograph exhibits the fusiform shape of the 
lacunas in the lamellas, and the rounder spaces elsewhere; also the connective 
tissue stroma of the matrix. 



(iii) Hard Palate 

Vertical antero-posterior sections of the roof of the mouth 
at the articulation of the palatal process of the maxillary 
with the horizontal plate of the palate bones, near the sutural 
line, all reveal the characteristics of dense osseous tissue 
thickly crowded with lacunas and canaliculi (Fig. 174), and also 
several longitudinal spaces of large dimensions filled with 
marrow. The long axes of the lacunae are more or less parallel 
to the long axes of the cancelli. 



204 



THE ORAL TISSUES 




Fig. 175. — Radiating connective tissue fibres in the matrix of the bone of the wall 
of the maxillary sinus. Magnified 250 times. Unstained. 




Fig. 176. — Perforating fibres running lengthwise through the matrix of the bony- 
wall of the maxillary sinus. Magnified 800 times. Unstained. The cut 
extremities of descussating fibres appear as white, round dots. 



THE MAXILLARY AND MANDIBULAR BONES 205 

(iv) Nasal Wall of Antrum of Highmore 

Here, as in the bone which constitutes the floor of the canine 
fossa, the matrix is very coarsely granular, and contains in 
places long markings, which are evidently the remains of the 
connective tissue stroma (Figs. 175 and 176). The lacunae, 
which are exceedingly scanty, do not present the usual charac- 
teristics, being spherical or oval when viewed from above (Fig. 
177). Some are concavo-convex as seen in side section. Again, 
the canaliculi are but very indifferently formed. 




Fig. 177. — Abrachiate lacuna? amongst perforating fibres. Bone of antral wall. 
Magnified 250 times. 

(v) Angle of Mandible 

Examination of the structure of vertical transverse sections 
exhibits, best of all, the pervious parts of the bones, — the 
regular disposition of the Haversian systems, and the peri- 
pheric and interstitial lamellae. The first are not very nu- 
merous, and are seen mainly in cross section. The peripheric 
lamellae are comparatively long, and the line of demarcation 
between the individual lamellae very marked (Fig. 1 78) . Strong 
lines of calcified connective tissue fibres can be observed, here 
and there, closely welding together the interstitial lamellae 



206 



THE ORAL TISSUES 




Fig. 178. — Vertical section of the angle of the mandible; from a dried specimen. 
Magnified 50 times. Unstained. The section shows the general structure. 
At the upper part of the figure the long peripheric lamellae are seen at the free 
edge of the bone, with interstitial lamellae between the Haversian systems. At 
the lower part of the figure the commencement of the cancellous diploe-like portion 
is separated from the external surface by the dense layer of dark compact bone. 




Fig. 179.— General structure of the bone of the alveolus; from a recent speci- 
men. The cancellous spaces and contents are too darkly stained to show any 
structure. Magnified 40 times. Stained with fuchsin. 



THE MAXILLARY AND MANDIBULAR BONES 207 




Fig. i 80. —Transverse section of the alveolus in situ; from a dried specimen. 
Magnified 40 times. Stained with borax-carmine. In the upper part of the 
photograph is the free edge; below, the dentine and cementum, with the perio- 
dontal membrane intervening. 







i8r. — Perforating fibres of the alveolus, passing into the periodontal mem- 
brane. Magnified 800 times. Unstained. 



208 THE ORAL TISSUES 

even in_ bones of adult life (age thirty-five years). Internal to 
the free surface of the jaw, the cancellated tissue follows very 
much the lines already laid down. 

Vertical lateral preparations of the same, show absence of 
Haversian systems, but multitudes of lacunae and canaliculi, 
and many radiating bands of calcified fibres. 




Fig. 182. — Lacunas and canaliculi in the bone of the alveolar process. Magnified 
250 times. Unstained. 

(vi) Alveolar Process 

Here are found all the appearances of soft cancellous bone, 
with Haversian systems and lacunae well marked (Figs. 179 
and 182). The cancelli run longitudinally in the same direction 
as the long axes of the teeth. Osseous tissue is dense externally 
(see Fig. 180) ; and the perforating fibres are very strong and of 
great length (Fig. 181). 

The foregoing remarks refer to the greater portion of the 
bony structures. At the free gingival terminations, however, 
the alveolar process is so narrow, that there is no room 
to accommodate medullary spaces and Haversian systems. 
These are, therefore, usually non-existent. The external 
alveolar plate is considerably thinner than the internal alveolar 
plate: in neither, does the bone exhibit a typical appearance. 



CHAPTER XI 

A GROUP OF MINOR STRUCTURES. THE ABSORBENT 

ORGAN— THE DENTAL CAPSULE— THE GUM— THE 

LINING MEMBRANE OF THE ANTRUM OF 

HIGHMORE 

THE ABSORBENT ORGAN 

Microscopical Elements: — (i) Connective tissue stroma; (ii) Osteo- 
blasts; (iii) Foveolae of Howship. 

GENERAL CHARACTERISTICS 

Definition. — A delicate vascular structure spread over por- 
tions of the roots of the deciduous teeth of man, during the 
periods when they are about to be shed. 

Origin. — From the outer layer of the dental capsule of the 
permanent teeth. 

Macroscopical Appearances. — A thin, white, insensitive organ 
covering the excavated parts of the roots of deciduous teeth 
loosened by the impending eruption of their permanent suc- 
cessors. It can be easily removed from the dentine, but is best 
observed and studied when retained in situ. It may also be 
seen as a soft reddish papilla over the crowns of the erupting 
permanent teeth. 

HISTOLOGY 

Vertical sections exhibit a tissue composed of cells and blood- 
vessels imbedded in a dense connective tissue stroma. 

The cells are usually small and round, with round or oval 
prominent nuclei. On the surface, and filling the foveolae of 
Howship — large bay-like crescentic excavations in the dentine 



THE ORAL TISSUES 




Fig. 183. — The absorbent organ. Prepared by the Author's process. Stained 
with Ehrlich's acid haematoxylene. Magnified 40 times, o. Absorbent organ; 
D. Dentine of the deciduous tooth. 




Fig. 184. — Same as the preceding. Magnified 250 times, h. A Howship's 
foveola with its giant-celled occupant; d. Dentine of the deciduous molar. 



THE ABSORBENT ORGAN 



—are found large multi-nucleated giant cells which correspond 
in many particulars with osteoclasts. In fact, they may be con- 
sidered to be nothing more nor less than these specially organ- 
ised cells. The cells which make up the main mass of the 
organ are of the ordinary variety. They are not osteoblasts, 
in the general acceptance of the term, but may take on a lime- 
depositing function, as sometimes there are evidences in physio- 
logically absorbed roots of new depositions of dentinal matrix. 




- v mk 




Fig. 185. — The absorbent organ in situ. Prepared and stained as in Fig. 
153. Shows a deposition of dentine matrix (with a few scattered cells em- 
bedded in it) in the excavated portions of the dentine. Magnified 50 times. 
o. Absorbent organ; d. Dentine of deciduous tooth; m Dentinal matrix contain- 
ing nucleated cells; a. Albumenoid material undergoing calcification. 



In the two accompanying photomicrographs, Figs. 186 and 
187, it will be seen that a kind of hyaline matrix has been laid 
down, in the excavated portions of the roots of the deciduous 
teeth. This nearly homogeneous material may at times 
present nothing more than a coarse granularity, or, at times, 
show a finely fibrillated reticulum with large round nucleated 
connective tissue cells imbedded in its midst. Both forms 
closely recall those two kinds of adventitious dentine found in 
the pulp known as hyaline, and cellular (q.v.). Here, again, 



THE ORAL TISSUES 



is another remarkable instance of dentinal matrix being pro- 
duced without the aid of the so-called odontoblasts. 

The vessels are very numerous, but comparatively large 
nerves other than vaso-motor branches are probably absent. 





Fig. i 86. — A similar section to the preceding. Prepared and stained as in 
Fig 184. Magnified 250 times. H. The foveolae of Howship filled with cal- 
cified'dentinal matrix. 



THE DENTAL CAPSULE 

Microscopical Elements:— (i) Outer and Inner Portions; (ii) Fibres; 
(iii) Glands. 



GENERAL CHARACTERISTICS 

Definition. — A sac-like investment of fibrous tissue of the 
non-erupted teeth of man, and many animals, which disappears 
after histogenetic periods have passed. 

Origin. — From the mesodermic cells of the outer poition of 
the dentinal papilla. 

Macroscopical Appearances. — A rather tough, pale membrane 
easily stripped off the surface of teeth which have not yet 
arrived at the proper time for eruption. The author has been 



THE DENTAL CAPSULE 



2I 3 



unable to find another organ in the body which is its counter- 
part. It exists for a few years only, and when its work — that of 
protecting the crown of the erupting tooth, after being instru- 
mental in generating the cementum and periodontal membrane 
— is accomplished, it disappears entirely, completely differing 
from such organs as the uterine adnexa, which persist after the 
cessation of their functions, and even the thymus gland, which, 
as a rule, leaves traces behind. It can be fairly claimed for the 




Fig. 187. 



•Degeneration and vacuolation of the dental capsule prior to its 
disappearance. 



dental capsule that in this respect it is unique. Regarded from 
an embryological aspect, the dental capsule, e.g., of the first 
premolar, may be observed in certain portions of the oral sub- 
mucous and alveolar tissues about the ninetieth day of intra- 
uterine life in man, and can be well demonstrated in sagittal 
sections of the jaws of kittens three weeks old. The cells are 
very elongated and thin, with small lenticular nuclei, chiefly 
arranged in longitudinal bundles corresponding to the long axis 
of the tooth germ. Later on they become developed into the 



214 



THE ORAL TISSUES 



extended fusiform cells of fibrous connective tissue. Eventu- 
ally the capsule undergoes atrophy and degeneration by the loss 
of the nuclei of its cells and vacuolation of its substance, in this 
specific instance, about the seventh to the ninth year in man. 
This vacuolation, it is important to notice, occurs as a normal 




Fig. 188. — Sagittal section in the incisor and canine regions of mandible of 
a young heifer. Prepared by cutting through the jaw with a saw while in the 
recent state. Actual size. Shows (p) the permanent tooth in its (f) capsule; 
T. Functional deciduous incisor. 



change in the capsules of teeth about to erupt, of course just prior 
to their disappearance; but when a tooth is retained in situ in 
the bone, it does not follow that it undergoes this vacuolation. 

HISTOLOGY 



It is composed of bundles of white connective tissue fibres, 
running in a complex and varied fashion and interlacing in all 
directions. The cellular elements, as well as the vascular 



THE DENTAL CAPSULE 



215 



supply, are scanty. The outer portion is less dense than the 
inner, but it cannot be removed as a separate layer from the 
latter, as neither is divided by a pronounced line of demarca- 
tion. The inner is dense, and is covered on its free surface, i.e., 
the part directed towards the enamel and cementum with a flat 
layer of epithelial cells, which are manifestly part of the layer 
of polygonal cells of Nasmyth's membrane. 

Running inwards towards this cellular layer groups of 
tube-like epithelial bodies wind between the fibres. They are 




Fig. 189. — A tubular gland-like structure from the dental capsule of man. 
Prepared by "fixing," hardening, and cutting on an ether-freezing microtome. 
Stained with Ehrlich's acid hsmatoxylene. Magnified 250 times. 



simple in construction, though sometimes they may branch. 
They have no definite lumina; but the epithelial cells which 
line the basement membrane are cubical in shape and have 
large prominent nuclei. They end in culs-de-sac. Their 
function is unknown, and their origin doubtful, although it 
is quite possible that they may be derived originally from 
"rests" or vestigial remnants of the unatrophied epithelium of 
the tooth-band. 



2l6 



THE ORAL TISSUES 



THE GUM 

Microscopical Elements: — (i) Epithelium of the mucous membrane; 
(ii) Simple and compound papillae; (hi) Mucous glands; (iv)j Fat 
lobules; (v) Blood-vessels; (vi) "Glands" of Serres. 

GENERAL CHARACTERISTICS 

Definition. — The soft dense tissue which clothes the alveo- 
lar processes of the jaws, being intimately connected with their 
periosteum, and surrounding the necks of the teeth. 




Fig. 190. — The margins of the gingival tissue in an interdental space. Magni- 
fied 200 times. Stained with hasmatoxylene. o.e. Oral epithelium of the gin- 
gival tissue; D. and C. Dentine and cementum of two contiguous teeth, that on the 
left being hyperplasic. 

Origin. — The superficial epithelial portion is derived from the 
stomodaeal ectoderm, the submucous tissue from the stomodaeal 
mesoderm, both due to the backward involution of these parts 
of the blastoderm between the maxillary and mandibular 
processes of the head. 

This involution deepens and extends further backwards, 
till a thin partition only intervenes between it and the caecal 
extremity of the fore-gut. On the absorption of this, connec- 
tion with the pharyngeal cavity is permanently established. 



THE GUM 217 

Macroscopical Appearances. — The gum is a smooth, firm, 
pale pink tissue round the necks of the teeth, continuous 
externally with the sulci between the lips and cheeks, and 
internally with the hard and soft palates, floor of mouth and 
root and sides of tongue. The gum envelops the arches of the 
osseous septa between the teeth in much the same way, but 
not to so great an extent as over the external and alveolar 
plates (see Figs. 191 to 194). In normal conditions there are 
no interdental papilla?. 




Fig. 191. — Gingival tissue covering an interdental septum of bone, showing 
oral epithelium, and character of sub-epithelial parts. Magnified 200 times. 
Stained with hffimatoxylene. o.E. Oral epithelium; G.T. Gingival tissue; B.T. 
Free termination of alveolar bone; p. Periosteum. 



HISTOLOGY 

The minute anatomy of the gum may be conveniently 
considered under the following heads: (A) The mucous mem- 
brane; (B) The submucous tissue. 



A 



The mucous membrane, about 0.3 mm. thick, is essentially 
of a stratified epithelial character, consisting as it does of 



218 



THE ORAL TISSUES 




Fig. 192. — Another portion of the gingival tissues covering an interdental sep 
turn of bone. Magnified 200 times. Stained with haematoxylene. o.Ei. Normal 
oral epithelium; 0.E2. Deeper and more abundant oral epithelium; g.t. Normal 
gingival tissue. 




Fig. 193. — Gingival tissues covering another interdental septum of bone. 
Magnified 200 times. Stained with haematoxylene. o.e. Thin layer of stratified 
squamous epithelium; g.t. Normal gingival tissue. 



THE GUM 



219 















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Fig. 194. — Vertical section of the gum. Prepared similarly to Fig. 193. 
Stained with Ehrlich's acid hsematoxylene. Magnified 50 times, a. Oral 
epithelium; p. Papilla of the submucous tissue; c. Connective tissue fibres inter- 
lacing in all directions; d. Scanty cellular elements; v. Blood-vessel; t.t. Parts o 
the section bordering the gingival trough, torn in cutting; b. Alveolar bone. 



2 20 THE ORAL TISSUES 

several layers. On the surface are large, stratified, squamous 
epithelial cells which overlap each other to some extent. Deeper, 
they become more cubical in shape, but the deepest of all are 
columnar in outline, and form the rete Malpighii, resting on an 
exceedingly thin basement membrane. In the lower layers the 
shape of the cells is modified by their mutual apposition. 
They fit each other very closely. The epithelium of the gum 
can be divided into the layers known as the stratum comeum, 



WW 




1 



Fig. 195. — Vertical section of the oral epithelium. Stained with Ehrlich's 
acid hasmatoxylene. Magnified 250 times, o.e. Epithelium of gum (oldest 
cells); b.b. Intercellular bridges of the "spiny" cells; R. Rete Malpighii; C. 
Corium. 



stratum lucidum, and stratum granulosum, as in the epidermis, 
and possibly there is eleiden or granular material deposited 
in the older, more superficial cells. 

The deeper cells are more protoplasmic than the others, 
undergo repeated karyokinesis, and gradually push outwards 
the latter, which ultimately become lost by abrasion. 

Many "spiny cells," separated by systems of wide intercel- 
lular channels, are often noticed in the layers nearest to the 
rete mucosum or Malpighii. 



This last named consists of a very folded line of columnar 
cells, placed vertically on the surface of the papillae, which 
are formed by the submucous tissue. 

The epithelial mucous membrane is perforated here and 
there to allow the passage of the ducts of many mucous glands, 
which are present in the sub-lying region. 

The gingival tiough extends to a depth of 2.5 to 4 mm. in 
different situations, and always contains, even in the healthiest 
of mouths, microorganisms of the Micrococcus Catarr halts, and 
Streptococcus pyogenes groups. It is bounded internally by the 
enamel, externally by the stratified squamous epithelium of the 
gingival tissues. 

B 

The sub-mucous tissue consists of dense bundles of connective 
tissue arranged throughout its substance. These are closely 
associated with the fibres of the alveolar periosteum, and at the 
necks of the teeth, with the "principal" fibres of the alveolo- 
dental periosteum. They pass outwards in fan-shaped fas- 
ciculi to the surface of the numerous papillae. 

The latter are large elevations of the sub-mucous fibrous tissue. 
They form the base on which the cells of the rete mucosum rest, 
and between them are depressions which vary indefinitely in 
size and shape. A simple papilla consists of one large mound or 
elevation of vascular fibrous tissue, the term "compound" 
being applied to those larger ridges, which are further sub-di- 
vived by smaller ones passing in from without. The papillae are 
visible to the naked eye, if, after removal of the epithelium by 
means of some dissociating fluid, the free surface of the gum be 
examined. 

Among the connective tissue fibres plasma cells are frequently 
seen. These are large cells with round, eccentrically placed 
nuclei whose chromatin stains intensely. Their cytoplasm is 
dense and stains deeply. Occasionally they contain vacuoles, 
which when filled with semi-fluid substances are recognised as 
Russell's fuchsine bodies. Mast cells and leucocytes are often, 
also, found. 



222 THE ORAL TISSUES 

Other constituents of the sub-epithelial tissue are: — 
(i) Small lobules of fat cells — tiny oval vesicles (each cell 
being about 70^ in diameter) — of adipose material gathered 
together into clusters, and imbedded in a fine reticulum of 
areolar connective tissue; (ii) Mucous glands, similar to those 
described on page 189; (hi) Blood-vessels, which are abun- 
dantly distributed; (iv) Scanty nerve fasciculi; and (v) the so- 
called "glands" of Serres. 




Fig. 196. — Gingival tissue covering the internal alveolar plate of the incisor 
region of a woman of 25 years. Normal. Magnified 200 times. Stained with 
haematoxylene and eosine. o.e. Stratified squamous epithelium; a.b. Bone of the 
internal alveolar plate; m.g. Mucous gland; D. Duct of mucous gland. 



There are large mucous glands in the gum at the cervical 
margins of the teeth on the lingual or palatal side, none in that 
on the labio-buccal aspect of the alveolar process. The author 
experimentally proved this by excising a portion of normal gum 
immediately in contact with the teeth, on the outer side of the 
alveolar process of the mandible of a man, aged about forty* 
four, and chose a spot between the two right premolars. It 
measured 6.5 mm. in length. There was no mucous gland 
to be seen. Similarly none was present in the gum on the labial 
aspect of the bone over the root of the second left maxillary 



THE MAXILLARY SINUS 223 

incisor of a woman aged twenty-five. Again, in a piece of the 
tissue, over the septum which intervenes between two man- 
dibular molars, no mucous gland was found. The reason is 
obvious. Mucous glands are not wanted in the former situa- 
tion, because of the existence of countless numbers which open 
on the free surfaces of the lips and cheeks and in the latter 
situation because of lack of room. 

The "glands" of Serres (see Figs. 251 and 253), according to 
Tomes {op. cit. p. 126), are "small round aggregations of pave- 
ment epithelium, met with at a little depth, or even imbedded 
in the surface." These have no known function, but are rem- 
nants of the dental lamina or tooth-band. Bland-Sutton and 
R. R. Andrews 1 consider them to be histologically comparable 
to young enamel organs; but Sayre Marshall 2 erroneously 
describes them as lobulated glandular structures. 

THE MUCOSA OF THE ANTRUM OF HIGHMORE 

Microscopical Elements: — (i) Epithelium; (ii) Submucous Tissue; 
(iii) Glands. 

GENERAL CHARACTERISTICS 

The histology of this tissue seems to have escaped the notice 
of workers, who, generally speaking, have contented themselves 
by saying that it is continuous with, and similar to the Schnei- 
derian mucous membrane of the nose. 

A knowledge of its minute structure is important because of 
its intimacy with the roots of the first and second maxillary 
molars, or premolars, and the fact that treatment of its diseased 
conditions not infrequently comes into the province of the work 
of the dental surgeon. 

Regarding its anatomy, Sappey 3 describes it as being supplied 

1 "American Text-Book of Operative Dentistry," p. 00, 1901. 

2 "Principles and Practices of Operative Dentistry," p. 58, 1901. 

3 "Quant au sinus maxillaire, elles (the glands) repandent sur tous les points 
de ses parois avec une telle profusion, qu'il serait fort difficile d'en faire le 
denombrement. . . . Ces glandes affectent, du reste, toutes les dimensions et 
toutes les formes possibles: il y en a de tres considerables et de tres compliques, 
de moyennes, et plus simples, de petites, de tres minimes, et enfin d'uni-utricular. 
Les unes revetent la forme arrondie, d'autres la forme rameuse, d'autres les 
formes intermediares. Elles sont surtout remarquables par la dilatation 
extrement frequente de leur conduit, en sorte que sur un grande nombre, d'entre 
elles il existe un kyste, naissant, ou ayant deja acquis une certain developpment ou 
completement developpe." — "Traite d'Anatomie," Vol. III., Paris, p. 660, 1871. 



2 24 THE ORAL TISSUES 

with glands, which, in appearance, are much like the Meibo- 
mian glands of the eyelids. They are irregularly distributed, 
and much scantier than those of other mucous membranes. 
• Definition. — The lining membrane of the maxillary sinus, 
otherwise called the antrum of Highmore. 

■ Origin. — It is an outward involution of the ectoderm of the 
olfactory fossae, which themselves originate at a point below 
and in front of the ocular vesicle. It is said that it begins to 
develope about the fourth month of intra-uterine life. 

Macroscopical Appearances. — A thin whitish tough mem- 
brane, very readily removed from the bone, and in places 
thrown into slight rugae. In old subjects (at. 64) patches of 
pinkish material (inspissated mucus) may be seen. The thin- 
ness is not uniform, in health, large territories may be found 
somewhat thicker than the rest. It is also slightly thicker over 
the situations of the glands. 

It measures 0.7 mm. to 0.9 mm. in thickness. The whiteness 
is due to lack of blood supply, which is particularly scanty. The 
vessels come from the anterior and posterior ethmoidal branches 
of the orbital group of the ophthalmic artery. Bodecker, in this 
connection, says (op. cit.) "The blood-vessels are principally 
derived from the mucous membrane of the nasal cavity, 
although some of the smaller branches arise from the posterior 
dental arteries through the alveoli." 

Its toughness depends upon the large amount of white con- 
nective tissue fibres which go to make up the greater proportion 
of its bulk. Sections curl up very readily, and large pieces can 
be torn off the thin bony walls to which it is but loosely attached 
by fibrous tissue. 

HISTOLOGY 

The lining membrane presents for microscopical examina- 
tion — (i) An epithelial surface, (ii) sub-epithelial tissue, (iii) 
certain glandular structures, and (iv) its periosteal attachment. 

(i) The Surface Epithelium 

In common with the mucous membrane of the respiratory 
passages (except that of the olfactory region of the nose), the 



THE MAXILLARY SINUS 225 

upper surface of the soft palate, the nasal region of the pharynx, 
and several other organs of the body, the epithelium of the 
antral mucosa consists of a transitional layer of ciliated co- 
lumnar epithelial cells, situated side by side, and on and between 
several layers of variously shaped cells, the lowest stratum of 
which is placed on a delicate basement membrane. This cov- 
ers the whole of the mucous membrane. 

The layer of epithelium measures about 0.02 mm. in depth in 
young subjects (at. 25). 

Each superficial cell is granular, narrow, more or less colum- 
nar in shape, and bears, at its free end, a number of long cilia, 
which are securely fixed to the surface of a clear disc. The 
attached basal extremity of the cell is generally pointed or 
dichotomous. 

The intervening and deep-lying cells are pyriform or polyhe- 
dral, thus called, by some authors, "battledore cells," whilst 
the deepest cells are spherical. All have very pronounced oval 
nuclei, which in the case of the first-named is situated near 
the refractile disc. 

Some authors consider that the younger spherical cells finally 
replace those possessing cilia; but probably this is not true, as 
they appear to contain mucigen, and to become ultimately 
distended into the shape of goblet-cells. 

At intervals numerous goblet or chalice cells may be observed 
between their ciliated neighbours. 

These are large poculiform bodies, with wide open mouths, 
which are directed inwards towards the centre of the antrum. 
Each contains mucigen and an indistinct small nucleus placed 
at its distal end. The mucus may entirely or only partially 
fill it; but sometimes it can be observed in sections, becoming 
extruded from the mouth of the cell. 

(it) The Sub-Epithelial Tissue 

is very loose, and sparsely supplied with cells and blood-vessels, 
though glands are fairly abundant. It is. made up of bundles 
of white connective tissues fibres, which, while in no sense 
compactly arranged, are still very tough. The author has 



226 



THE ORAL TISSUES 



never noticed the presence of any elastic tissue fibres in this 
membrane. 

(Hi) The Glands 

are of great interest. They are visible macroscopically in 
suitably stained specimens, as pin-point spots more deeply 
coloured than the rest of the tissue. Seen in sections cut in a 




Fig. 197. — A mucous gland of the lining membrane of the antrum of High- 
more. Stained with Ehrlich's acid haematoxylene, counter-stained with eosine. 
Magnified 250 times, a. Mucous secreting cells in activity; r. The same after 
the period of activity is passed; c. Crescent of Gianuzzi. 

plane perpendicular to the surface of the bone of the antrum, 
they present the appearance of tubular glands; and this, no 
doubt, led Sappey to assert that they resemble the Meibomian 
glands in the eyelids. Such, however, is not the case, for if 
sections be made in an oblique direction, or in a plane parallel 
with the surface of the antral bone, below the level of the 
epithelial layers, they are at once recognised as compound 
racemose bodies, consisting of well-defined lobules, and having 
single ducts, which open on to the free surface of the mucous 
membrane. 



THE MAXILLARY SINUS 227 

The largest glands measure in length 0.8 mm. to 1.3 mm., 
and 0.2 mm. to 0.6 mm. in depth. The lobules assume varying 
shapes (see Fig. 197), and are held together by delicate strands 
of connective tissue. Each lobule possesses a small duct, which 
communicates with a larger excretory duct, and its constituent 
parts are composed of a number of alveoli or acini. Glands 
during rest, and after a period of activity, are clearly observed. 

These latter consist of a basement membrane, on which 
rest, by means of their broad bases, five or six, or more, large 
polygonal secretory cells. Others often fill the acini, leaving 
but little room for lumina. Their translucent interiors are 
traversed [by an exceedingly minute reticulum of fibrils, 




Fig. 198. — Diagram of Fig. 197 shows the secreting mucous cells about to begin 
their functions. Several crescents of Gianuzzi can be seen. 



which includes in its meshes mucigen, small indifferent flattened 
nuclei being placed at the periphery of each cell. The crescents 
or lunulae of Gianuzzi — groups of small crescentic granular 
nucleated bodies — may be found occasionally in places between 
the bases of the cells, more darkly stained than the other parts 
of the acini. 

The ducts are short, straight tubes, of about 0.02 mm. in 
length. In width at their orifices they may measure as much 
as 1 mm. At their junctions with the gland substance proper 
their diameters are less, as they are somewhat truncated. 
They are lined with a simple layer of small cubical epithelial 
cells. 

{iv) The Periosteal Attachment 

is due to the presence of strong bands of connective tissue which 
pass into the peripheric laminae of the bone. 



PART III 

THE HISTOGENESIS OF THE TEETH OF 
MAMMALS, FISHES AND REPTILES 



CHAPTER XII 

THE DEVELOPMENT OF THE TEETH IN MAMMALIA 

Microscopical Elements in: — (i) The Enamel Organ; (ii) Dentine Germ; 
(iii) Dental Capsule, (iv) During later periods of the formation and 
growth of the enamel, dentine, and cementum; and (v) Appear- 
ances in human embryos at half term. 

For purposes of description it will be convenient to divide 
the series of phenomena which take place during the histo- 
genesis of the deciduous and permanent teeth and surrounding 
structures, into: 

(A) The changes occurring in the jaws before and up to 
the period of formation of the dentine germ, 

(B) The metamorphoses occurring in and around the tooth 
germ at the period of formation of the dentine germ, 

(C) Subsequent stages of development. 



Earliest Phases of Evolution 

At a very early period of intra-uterine life in man, viz., 
about the 40th to 45th day, the embryo measuring about 12 cm. 
in length, the first signs of change are noticeable. The date 
synchronises with the commencement of ossification of the 
clavicle, the first of all bones to ossify. 

(i) Changes in the Ectoderm 

Coronal sections through the anterior part of the embryonic 
head before this age show that there is a slight appreciable 
thickening of the stomodaeal ectoderm over the regions of the 
231 



232 DENTAL HISTOGENESIS 

embryonic alveolar processes, that is, the promontories of 
tissue known as the maxillary processes of the embryonic face, 
which, having met the lateral plates of the fronto-nasal proc- 
ess, have continued their growth downwards and inwards, 
and joined the mid-frontal process to complete the alveolar 
arch and maxillary bone. In the mandibular arch the changes 
begin above the cartilage of Meckel, and at places a little 
external to the primitive elevation of the tongue. 




Fig. 199. — Coronal section through head of a human embryo, exact age un- 
known. Prepared as other soft tissues. Stained en masse with borax-carmine, 
and cut in paraffin wax. Magnified 20 times. To show the development of 
the maxilla?, m.p. Maxillary process; m.f.p. Mid-frontal process; l.p. Lateral 
plates of fronto-nasal process. 

The contour of the rete Malpighii is undisturbed in its clear 
outline and flattened appearance. 

The epithelial surface of the mouth is extremely thin and 
undeveloped, consisting of a few flat cells, while the rete Mal- 
pighii is almost indistinguishable from the rest of the ectoderm. 
A great depth in the mucosa is noticed, and the bones which 
will ultimately form the crypts of the teeth are beginning to 
appear and stain deeply. 



development of teeth in Mammalia 



233 



In the kitten, the start in the development of the bony 
alveoli is delayed at this time, and even later; but in man, 
the osseous framework begins to assume a somewhat different 
shape, and is a prominent feature in specimens of an earlier 
date than the 40th day. 

At this age, however, a marked metamorphosis in the 
ectoderm can be observed. 




Fig. 200. — Coronal section through head of embryo of cat. Prepared and 
stained as last figure. Magnified 20 times. Represents the stage of develop- 
ment in man at about the 50th day of intra-uterine life. t.G. Tooth germ; 
z. Tooth band; l.f. Lip-furrow; t. Tongue; m. Meckel's cartilage; b. Commence- 
ment of formation of bone of alveolus. 

(ii) Formation of the Dental Furrow 

Its free surface appears to be slightly indented (" The primi- 
tive dental furrow"), in most cases, and follows fairly closely 
the lines of contour of the rete Malpighii. Over the palate 
in places, it is one cell thick, but over the floor of the buccal 
cavity, as well as its sides, and the sides of the roof, four, 
five, eight, or even nine rows of cubical or polygonal cells 
can be counted. The large size of their oval nuclei arrests 
attention. The cubical cells are set on what looks like a 



2J4 DENTAL HISTOGENESIS 

delicate line or basement membrane. A few small flat squa- 
mous cells are often found here and there, coherent to the 
surface epithelium. 

As the epithelium approaches the place where the primary 
inflection is about to occur, it becomes thickened. 1 The nuclei 
become considerably elongated, and almost fill the cells which 
themselves have undergone some amount of lengthening. 

The epithelial surface is clearly distinguishable from the 
underlying tissues, for two reasons: — It takes the stain more 
intensely, and its cellular constituents are crowded together. 
In other words, its appearance is identical with that which 
is about to form the Schneiderian membrane of the nose, the 
surface epithelium of the skin of the face, and the under surface 
of the tongue. 

The ectoderm would appear to be formed some considerable 
time after the mesoderm, that is, it is an involution of the 
superficial layer of the blastoderm reflected backwards into 
the mesoderm. Its genesis is probably synchronous with that 
of the nasal fossae, external skin, and mucous membrane of 
the cheeks. 

(iii) The Primary Epithelial Inflection 

In coronal sections of the maxillae the first epithelial in- 
volution into the subjacent mesoderm begins at a spot a little 
external to the lateral margins of the tongue, in the mandible 
some distance internal to those margins. The invagination 
extends right round the jaws, and thus forms a continuous 
semi-circular band of cells enclosed by mesodermic tissue. 
In vertical sections it looks like a narrow finger-like penetra- 
tion of cells into the mesoderm: in side section it is seen to 
be a continuous flat band extending from the surface into the 
jaw. 

(i) Origin of the Lip-furrow and Tooth Band 
At the 4o-45th day a splitting of this primary inflection 
occurs, not across, but in a longitudinal direction with it; thus 

1 This epithelial thickening is greatest along the line of the future jaw on the 
surface of which it extends longitudinally, and is produced by sub-division and 
repeated multiplication of the deepest cells. 



development of teeth in Mammalia 235 

it becomes divided into two parts, an outer and an inner. 
The former is towards what will be the labial side, the latter 
towards the tongue. The former, known as the labio-dental 
strand, or lip-furrow, passes in a perpendicular direction, 
and ultimately produces the groove which is afterwards the 
furrow between the lips and the alveolar processes of the jaws: 
while the latter, known as the common dental germ, or tooth 
band, is penetrating the mesoderm in a horizontal direction, 
and becomes the layer of cells, in connection with which both 
the deciduous and permanent teeth are developed. 



Fig. 201. — Diagram to show method of cleavage of the primary epithelial 
inflection, e.l. Ingrowth of epithelium; l.f. Lip-furrow on outer or buccal side; 
z. Tooth band on lingual side; f. Free growing end whence the permanent tooth 
germs will arise. 

The opposing theories regarding the relations to each other 
of lip furrow and tooth band may be, here, briefly noted. 
Thus: 

(i) Rose 1 affirms that both have a common origin, as just 

described. 
(ii) Baume 2 believes that the tooth band arises from the 
side of, or is merely a process of the lip furrow, an 
opinion shared also by 
(iii) Xavier Sudduth, 3 who says: — "The lamina is only 
an offshoot from the side of the band, which becomes 
somewhat shallower, and in some instances disappears." 
(iv) Leche 4 holds that both are developed separately, but 
simultaneously. 

1 " Archiv. f. mikros. Anatomic" Bd xxxviii, 1891, and "Anat. Anzeig," 1896. 
2 "Versuch einer Entwickelungsgeschichte des gebisses," in Odontologische 
Forschungen, 1882. 

3 "American System of Dentistry," p. 620, 1887. 

4 "Morph. Jahrbuch, " 1892, and "Bibliotheca Zoologica," 1895. 



236 



DENTAL HISTOGENESIS 



At this time the tooth band possesses an attached edge or 
border, which is continuous with the surface epithelial cells, 
and a free edge or border, which penetrates more deeply inwards. 
It is from this free edge that the ten deciduous tooth germs 
in each jaw will be developed. 

Still examining the coronal sections through the embryonic 
head, it is seen that each tooth germ is accurately directed 




Fig. 202. — Diagram of a sagittal section through the germ of the first man- 
dibular milk molar of a human embryo 30 mm. long. o.e. Oral epithelium; 
L.F. Lip-furrow; z. Tooth band; p. Site of future dentine germ {After Rose.) 




FL P 

Fig. 203. — Diagram of a similar section to the preceding figure, but through 
the germ of the canine tooth of an embryo 40 mm. long. The lettering as in Fig. 
202. (After Rose.) 



towards the central portions of the developing alveolar bone: 
thus the direction of growth in the maxilla is upwards and 
slightly inwards, that in the mandible is downwards and slightly 
inwards. (See Figs. 200 and 204.) 

The cells lining the tooth band possess the same histological 
characteristics as those at its immediate junction with the 
free stomodaeal epithelium; viz., long, cylindrical cells with 
large oval granular nuclei situated rather more towards the 
distal than the basal end. 

They are placed side by side in a single layer, the substance 
of the tooth band being composed of round or polygonal less 
distinct cells having circular, less granular nuclei. 



development of teeth in Mammalia 237 




Fig. 204. — Coronal section of the mandible of an embryonic pig. Stained 
with haematoxylene. Magnified 45 times. Represents the stage of development 
in man at about the 50th day. z. Tooth band; l.f. Lip-furrow; o.e. Epithelium 
of mouth; M. Meckel's cartilage; b. Bone of alveolus. 




Fig. 205. — Further stage of growth. Magnified 45 times. The tooth germ 
in the centre of the field represents the stage of development in man at about 
the 60th day. e.o. First evolution of enamel " bud." Lettering as in preceding 
photomicrograph. 



238 DENTAL HISTOGENESIS 

(v) Changes in the Mesoderm 

Coincidentally with these alterations of the epithelial sur- 
face, many, not all, of the cells of the mesoderm (hitherto dis- 
crete) in the immediate proximity of the growing extremity 
of each germ undergo three distinct and remarkable changes. 
First they lose their identity as spherical mesodermic cells with 
rounded nuclei; they undergo a fresh arrangement of position; 
they become multiplied in numbers. No longer do all the 
mesodermic cells share like features regarding shape, the new 
change being that many become elongated, and therefore 
spindle-shaped and have fusiform nuclei. Those nearest the 
rete Malpighii of the tooth germ retain for some time longer 
their rounded outlines. Their new position is one in which 
their long axes take up the same direction as that of the up- 
growing tooth germ. Their numbers are trebled or quadrupled. 
It must not be forgotten, however, that these phenomena are 
only to be observed at the developing end of the epithelial 
germs. 

(vi) Evolution of the Enamel Organ 

The next step in development is concerned with the deepen- 
ing of the tooth band and its lateral expansion near, but not 
at, its free end, into a bell-like structure. This takes place at 
its deepest portion, and on its labial side. At the superficial 
part a slight constriction begins to take place; and at about 
the 60th or 70th day in man, the first rudiments of the enamel 
organs of the deciduous teeth in the incisor region can be clearly 
discerned. They are called " enamel buds." 

At certain spots, ten in number in either jaw, and separated 
at equal intervals along the continuous tooth-band these cam- 
panular bodies are found. The intervening portion of the 
tooth band in its anterior part presently atrophies and finally 
disappears after the lamina has become cribriform, 1 while it 

1 Unatrophied portions of the tooth band frequently persist. According to 
their growth they may develop into elongated epithelial masses in the dental 
capsule, "glands" of Serres, supernumerary teeth, enamel nodules, accessary 
cusps, true geminated teeth, or epithelial odontomes. 



development or teeth in Mammalia 



239 



still remains continuous in the posterior or molar region. The 
primitive enamel organs become now specially organised and 
constituted. 

Thus originate the earliest aspects of the enamel organ. In 
shape such an organ is primarily like a Florence flask or labora- 
tory beaker, having a broad flattened concave base, and long 
narrow neck opening on to the free surface of the epithelium 




Fig. 206. — Further stage of development. Magnified 45 times. Represents 
the stage of development in man at about the 70th day. d.p. Rudiments of 
dentine papilla. Lettering as before. 



of the mouth. At first the outline of the enamel organ is 
smooth, but later on, the external part will become rather 
sinuous, due to several "tufts" or "papillary projections" 
from the subjacent tissue indenting the external epithelial 
layer of cells. Sometimes the tooth bands and the necks of 
the enamel organs also exhibit these as collections of polyhedral 
cells similar to those just mentioned (see Fig. 232). Capillaries 
from the dental capsule are freely distributed to these "tufts." 
In structure, the external cells still assume a cylindrical 
character; the deepest are more pronounced than those else- 



24-0 



DENTAL HISTOGENESIS 



where, and they are still continuous with the oral rete Malpighii. 
The interior is filled with round cells, which however speedily 
develop long branched extremities, and exhibit, in a rudi- 
mentary fashion, the cells of the stellate reticulum. It is not 
yet determined how these internal cells become branched, or 
exactly in what way the stellate reticulum is formed. Some 
observers, including Tomes, have thought that they represent 
cells undergoing retrogressive changes — conditions which point 




Fig. 207.— Campanular form of tooth germ, from the jaw of an embryonic 
kitten. Stained with haematoxylene. Magnified 45 times. Represents the 
stage of development in man at 70th day. Lettering as before. 



to their ultimate disintegration and atrophy; 1 butLeon Williams 
holds that they merely represent a sort of intercellular stroma. 
It is nevertheless certain that lengthy 'marked' branching proc- 
esses unite them together, their nuclei, in early stages of 
growth, being in no degree diminished in size, shape, or position. 
All the central cells do not become changed into stellate 
bodies. Certain numbers, close to the deepest layer of the 

1 Cf. The degenerating cells in the cysts of epithelial odontomes, described 
in Chapter XV, Vol. II. 



development of teeth in Mammalia 241 

external epithelium, still retain their rotundity, and are ulti- 
mately the cells of the stratum intermedium which will presently 
assume their completed shape, viz., that of small polygonal 
rather branched cells, having connections externally with the 
stellate reticulum, and internally with the internal epithelium. 

Rapid growth now occurs at the margins of each organ, 
and the whole structure resembles a bell with a handle. 

The nearest mesoderm cells, about this time (70th day in 
man) begin to proliferate and to be more closely approxi- 




Fig. 208. — Diagram of a section through the germ of the first milk molar 
of a cow's foetus, 47 mm. long. z.vv. Heaped-up epithelium characteristic of 
ruminants; e.p. Enamel organ; p. Site of future dentine germ. {After Rose.) 



mated, and eight primitive dentine germs are noticed in the 
concavities of the enamel organs. 

The alveolar crypts of the anterior parts have become in- 
creased in depth and importance, and begin now to assume a 
definite poculiform shape. 

B 

The Metamorphoses Occurring in and around the Tooth Germ at 
the Period of Formation of the Dentine Germ 

The elongation of the necks of the enamel organs, the trans- 
parency of its central portions, the density of the dentine 
papilla, and the first attempts in the formation of a capsule 
or follicle or investing connective tissue sheath, are now ob- 
served (about 100th day). 



242 



DENTAL HISTOGENESIS 



While the neck of the enamel organ extends more deeply 
than ever into the jaw, it becomes still further constricted, 




Fig. 209. — Structure of enamel organ. From jaw of a newly born kitten. 
Stained with borax-carmine. Magnified 300 times, o. Odontoblasts; d. 
Dentine; a. Ameloblasts; s.m. Stratum intermedium; s.r. Stellate reticulum; 
e.e. External epithelium; d. p. Dentine papilla; d.c. Rudimentary dental capsule; 
a.l. Bone of alveolus. 



and practically occluded by the apposition of opposite rows of 
cells. 



development or teeth in Mammalia 243 




Fig. 210. — Section of incisor of a rat. Magnified 80 times, a. Capillary 
loops torn out of the secreting papillae; b. Secreting papillae after removal of 
capillary loops; c. Ameloblasts; e. Enamel; d. Dentine. {Photomicrograph by 
Leon Williams.) 




Fig. 211. — Secreting papilla? and ameloblasts from enamel organ of rat. 
Magnified 600 times. A. Papilla showing secreting cells; B. Showing roots of 
ameloblasts passing into papilla; c. Ameloblasts containing oval nuclei; D. 
Plasmic strings and granules emerging from ameloblasts. (Photomicrograph by 
Leon Williams.) 



244 



DENTAL HISTOGENESIS 



The stellate reticulum 
development. 



now near its fullest height of 



(vii) Structure of the Enamel Organ 

The periphery of the enamel organ, starting at the neck 
(at one side) consists of several rows of cubical or cylindrical 
epithelial cells, whose oval nuclei almost fill the whole cell. 
At this spot the most external stellate reticulum cells are flat- 




D P 
Fig. 212. — Later phase of development. Jaw of kitten. Stained with 
carmine. Magnified 65 times. Represents the stage of development in man at 
the 85th day. z. Tooth band of permanent germ; e.o. Enamel organ; d.p. Dentine 
papilla of deciduous tooth; d. Earliest trace of formation of dentine; o.e. Oral 
epithelium. 

tened and fusiform, and probably represent immature stellate 
cells, but their transition to the normal shape is sudden and 
pronounced. 

At the deepest part of the enamel organ many ovally nu- 
cleated cylindrical cells are seen, several layers thick. Passing 
over the convexity of the dentine germ they become aggregated 
more closely till, as a palisading, they are most elongated 
directly over the summit of the convexity. Above these cells 



development of teeth in Mammalia 245 

of the internal epithelium are now six or seven rows of rounded 
nucleated cells. It is possibly their function to recruit the 
former. 

Thus beginning from without inwards, the enamel organ 
consists of (i) external epithelium; (ii) stellate reticulum; (iii) 
stratum intermedium; and (iv) internal epithelium. The latter, 
soon to be called ameloblasts or enamel cells, are placed side 
by side on what would seem to be a fine basement membrane. 
There is no commencement of deposition of enamel. 

The cells of the stratum intermedium, according to Leon 
Williams, form a layer in which blood-vessels are developed 
at a very early stage. This is well brought out in the enamel 
organs of rodents. Here the layer seems to be "a highly 
differentiated secreting tissue." The ameloblasts are sur- 
mounted by epithelial papillae, around and between which is 
a free distribution of capillary loops. The enamel-forming 
cells are seen to have an intimate relationship with the papillae, 
each apparently having a root-like process which extends into 
and is lost within the papilla to which it belongs. "The 
diameter of each papilla is equal to about that of five or six 
ameloblasts, and each papilla may therefore be said to supply 
from twenty to twenty-five ameloblasts" (Fig. 211). 

The papillae are supposed to originate in spindle-shaped 
cells. 

(viii) Changes in the Dentine Papilla 

Meanwhile the dentine germ is becoming highly spe- 
cialized. The round nuclei of the cells crowd together, and 
apparently are imbedded at the enamal surface in a clear 
indefinable matrix. The cells are protoplasmic, minus 
branches; but most deeply of all they become fusiform with long 
branching processes, and are continuous with similar cells 
situated immediately outside the neck and the rotundity of 
the enamel organ. Furthest from the centre they are very 
narrow, and greatly separated from one another. 

The alveolar bone is, at this time, extending towards the 
surface, and is encroaching on the neck of the enamel organ. 



246 



DENTAL HISTOGENESIS 




Fig. 213.— Further stage of evolution. Jaw of kitten. Stained with haema- 
toxylene. Magnified 60 times. Represents the stage of development in man 
at about the 90th day. d.p. Dentine papilla; s.r. Stellate reticulum. 




Fig. 214. — Same as preceding, further developed. Same magnification. 
Represents the stage of development in man at about the 120th day. e. First 
trace of enamel; d. Calcified dentine; d.z. Dentogenetic zone; d.p. Dentine papilla; 
d.c. Dental capsule; a. Ameloblasts. 



development or teeth in Mammalia 



247 




Fig. 215. — Similar to the preceding. Stained with hasmatoxylene. Magnified 
80 times. Represents the stage of development in man at about the 100th day. 
e.e. External epithelium of the enamel organ; s.r. Stellate reticulum; s.l. 
Stratum intermedium; a. Ameloblasts; d.p. Dentine papilla; z. Tooth band of 
permanent successor; b.v. Blood-vessel; d.c. Dental capsule; a. b. Alveolar bone. 



2 4 8 



DENTAL HISTOGENESIS 




Fig. 216. — Vertical section through head of Macropus Billiardieri. Stained 
with hasmatoxylene and eosine. Magnified 45 times. There is no permanent 
tooth band, as Marsupials are mon phyodont. d. Dentine;D.p. Dentine papilla; 
S R. Stellate reticulum; n. Neck of enamel organ; B. v. Blood-vessel; v. m. Voluntary 
muscle of cheek; t. Tongue; o.e. Oral epithelium. 



development of teeth IN Mammalia 



249 



Shortly after these changes have taken place, the neck of 
the enamel organ is attenuated to the thickness of two layers 
of cells; and a tremendous increase in the mass of the stellate 
cells occurs. The internal epithelium assumes the shape of 
the ameloblasts, and some of the peripheral papilla cells that 
of the odontoblasts. 




o E 



X 




DP^S 



Fig. 217. — Further stage of development. Jaw of kitten. Stained with 
haematoxylene. Magnified 50 times. Represents the stage of development 
in man at about the 140th day. e. Early formation of enamel; a. Ameloblasts; 
D. Dentine; o. Odontoblasts; z. Tooth band of permanent successor; O.e. Oral 
epithelium; d.p. Dentine papilla; b. Bone of jaw; d.c. Rudimentary dental 
capsule. 

At the same time, about the 140th day in the deciduous 
incisors, the first deposition of formed dentine is seen, fol- 
lowed almost immediately by the darker fine of enamel. The 
external and internal epithelia are still continuous. 



Subsequent Embryological Changes 

The tooth germ, at a later stage, is lodged in a deep, wide- 
mouthed gutter of bone. The cap of calcified enamel is sur- 



250 



DENTAL HISTOGENESIS 



rounded by the layer of ameloblasts — long columnar proto- 
plasmic cells having prominent nuclei at their distal growing 
ends. They measure about 5^ in width, and vary in length 
from 5/x to 15 or 20/01. At the base of the dentine germ they 
are cubical in shape, and here attain the former smaller 
dimensions. 




Fig. 218. — To show early stage of formation of enamel and dentine. Pre- 
pared by the chromic acid method, stained with carmine, and imbedded in 
paraffin-wax. Magnified 320 times, d.p. Dentine papilla; o. Odontoblasts; 
d. Dentine; e. Enamel; a. Ameloblasts; t. p. Tomes' processes of the ameloblasts; 
s.m. Stratum intermedium; s.r. Nuclei of cells of stellate reticulum. (Photo- 
micrograph by Douglas Cabell.) 



In places where they are torn away from the periphery of 
the enamel they present tapering processes, "Tomes' processes." 
This end (viz., that directed towards the dentine), according 
to Tomes (op. cit. p. 168), is slightly enlarged, a fact demon- 
strated after treating an embryonic tooth germ with glycerine 
or other hygroscopic reagent. The cytoplasm of each amelo- 
blast is granular, and possesses also a delicate spongioplasm 
(see Fig. 240). 

Many instances occur in which the cells appear to be bounded 



development of teeth IN Mammalia 



251 



at either end by lines of basement membrane. To these Leon 
Williams has given the names the "inner and the outer amelo- 
blastic membranes." 







1 ^- '.: V. >- 




Fig. 219. — Section of developing tooth of human foetus near the seventh 
month of intra-uterine life. Magnified 175 times, a. Outer epithelial layer of 
enamel organ in which secreting papillae are developed; B. andc. Numerous large, 
round, granular, nucleated cells of reticulum of enamel organ. The stellate 
appearance in this tissue is largely produced by shrinkage and the washing 
away of the cell contents; D. Stratum intermedium; e. Outer ameloblastic 
membrane; f. Ameloblasts; G. Inner ameloblastic membrane; h. Dentine; i. 
Odontoblasts. (Photomicrograph by Leon Williams.) 



The former had been previously described by Huxley, Rasch- 
kow and others as the membrana preformativa. 

Both membranes are structureless basement membranes, 
and are adherent to both extremities of the ameloblasts. 



252 



DENTAL HISTOGENESIS 



The outer lies between the ameloblasts and the cells of the 
stratum intermedium; the inner between the ameloblasts 
and the formed enamel. 

Leon Williams describes these membranes very carefully 
in his contribution to The Dental Cosmos for 1896, pp. no 




Fig. 220. — Section of developing tooth of embryo calf. Magnified 800 times. 
a. Outer ameloblastic membrane; b. Ameloblasts showing network pattern of 
plasmic cell contents; c. Strings of plasmic network passing through inner 
ameloblastic membrane; d. Dentine; e. Chromatin of nuclei of odontoblasts; 
F. Spongioplasm of odontoblasts. (Photomicrograph by Leon Williams.) 



et seq.: "It is impossible at present (1896) to speak definitely 
with reference to its (the outer membrane) origin, exact struc- 
ture, or function. Its appearance at the ends of the cells and 
not between them would seem to argue against the suggestion 
that it is due to a condensation of the peripheral zone of the 



development of teeth in Mammalia 



253 



cells. But this view is supported by the fact that it is not seen 
during the earlier periods of the tooth germ; but only after the 
nearly or quite complete specialization of the ameloblasts." 
Under high powers it is composed of more than a single layer; 




Fig. 221. — To show arrangement of parts in the enamel organ. Stained 
with hEematoxylene. Magnified 300 times, d. Dentine; e, Enamel; a. Amelo- 
blasts; 1. Inner ameloblastic membrane; o. Outer ameloblastic membrane; 
s.m. Stratum intermedium; s.r. Stellate reticulum. 



and "it is possible that it plays an important part in the elabora- 
tion of material for enamel building. It varies considerably 
in thickness in different specimens, but persists throughout the 
entire period of enamel formation — a fact which would seem 



254 



DENTAL HISTOGENESIS 












IP 






Fig. 222. — Section of developing tooth of human embryo. Magnified 1,000 
times, a. Cells of stratum intermedium showing structure of nuclei, b. 
Ameloblasts; c. Enamel-globules showing radiating processes; D. Dentine; e. 
Odontoblasts showing chromatin of nuclei. (Photomicrograph by Leon Williams.) 



development or teeth in Mammalia 255 

to give a decided negative to the theory that the ameloblasts 
are renewed from the stratum intermedium, as many writers 
on the subject have supposed." 

The free surface of enamel has a pitted or honey-combed 
outline, whence the Tomes' fibres have been withdrawn; the 
rest is almost homogeneous. 




Fig. 223. — Similar to Fig. 221. p.s. Pitted surface of enamel; c. Calcoglobular 
mass in an ameloblast. 



Not so, however, the dentine, for traces of its tubular nature 
can, even at this early stage of growth, be easily observed in 
sections stained with Ehrlich's acid haematoxylene in its cal- 
cified (external), and less clearly in the formed but as yet un- 
calcified portions. 

The superficial mesodermic cells of the papilla, before the 
formation of the odontoblasts, are arranged with a certain 
amount of regularity, with their long axes pointing towards 
the ameloblasts. These in their growth become elongated, 
the result being, according to Paul {op. cit.), the formation of 
a definite superficial zone. 



256 



DENTAL HISTOGENESIS 



Their nuclei are "resting" (see Fig. 10 1). 

Later on the odontoblasts themselves begin to appear 
among these superficial cells, the nuclei of which, passing 
from the resting stage, undergo atrophy. 

The remainder of the papilla is made up of branched con- 
tinuous cells. 

Shortly after the fusiform connective tissue cells, which go 
to make up the dental capsule or follicle, have become con- 




Fig. 224. — Vertical section through mandible of human foetus at about the 
160th day of intra-uterine life. Shows base of decidnous canine tooth: Pre- 
pared as usual with soft tissues. Stained en masse in borax-carmine. Cut in 
paraffin-wax. Magnified 50 times. B. Base of dentine papilla; h. Epithelial 
sheath of Hertwig. 



tinuous round the whole tooth germ, the investing stellate 
reticulum begins to disappear. The first stage in its atrophy 
and absorption is the disappearance of the nuclei of these 
cells. 1 The external epithelial cells become somewhat separated, 
but connected still with the branches of the stellate reticulum 



1 The stellate reticulum persists longest in the intervals between the cusps of the 
molar teeth. 



development OF teeth in Mammalia 



257 



on the one hand and the elongated cells of the dental capsule 
on the other. The ameloblasts reach their highest degree of 
development over the cusps of the dentine germ, and the 
enamel is being rapidly manufactured. The dentinal wall of the 




Pig. 225. — Vertical section through jaw of pulp at birth. Prepared in the 
usual way. Stained with Ehrlich's acid haematoxylene. Magnified 45 times. 
Represents the stage of development in man at about the 140th day. o.e. Oral 
epithelium; a. Ameloblasts; e. Enamel; d. Dentine; o. Odontoblasts; d.p. Dentine 
papilla; s.r. Stellate reticulum; e.e. External epithelium; d.s. Dental capsule; B. 
Bone of jaw; p.z. Tooth band of permanent tooth germ; M. Voluntary muscle 
fibres cut transversely. 



tooth germ is lengthening towards the base of the dentine germ, 
which shows signs of constriction by the approximation of the 
cells of the internal epithelium. 

At the extreme point they suddenly curve upwards and 
outwards, and thus form the epithelial sheath of Hertwig. 



258 



DENTAL HISTOGENESIS 



The cells of the dentine germ possess the same histological 
characteristics, except those on the surface of the pulp, which, 




Fig. 226. — Coronal section through the maxilla of a fcetal pig. Prepared ; 
stained as in last figure. Magnified the same. Represents the stage of develop- 
ment in man at about the 120th day. Lettering as in Fig. 225. 



as the so-called odontoblasts, are clearly differentiated in 
size, shape, and staining properties from the other connective 
tissue cells. 



development of teeth IN Mammalia 



259 




Fig. 227. — Coronal section through the mandible of a kitten. Stained with 
borax-carmine after hardening in formic aldehyde. The blood-vessels are 
naturally injected. Represents the stage of development in man at about the 
i6othday. Magnified 65 times, e. Enamel; d. Dentine; s.r. Stellate reticulum; 
p.v. Blood-vessels in the pulp; l. Loops of capillaries extending to the external 
epithelium of the enamel organ. 



260 



DENTAL HISTOGENESIS 




Fig. 228. — Vertical section of mandible of pup at birth. Stained with 
h asmatoxylene. Magnified 30 times. About same age as preceding figure. 
r Early formation of a root; m.n. Mandibular nerve, with accompanying 
artery and veins. 



development of teeth in Mammalia 261 



(ix) Evolution of the Permanent Tooth Germs 

About this period sections show the epithelial inflection 
which goes to form the successional tooth, which is but the 
growing or free end of the tooth band, and not a budding 
from the neck of the enamel organ of the deciduous tooth 
germs. Rose has proved this fact beyond doubt. This 
neck has now completely vanished. 

Subsequently the tooth germ assumes the shape of the 
future tooth. The enamel organ has gone; the calcified den- 
tine and dentogenetic zone surround the young pulp. The 
thickness of the enamel cap has increased; the regularly 
arranged ameloblasts and stratum intermedium cells are very 
pronounced, and nothing intervenes between the oral epi- 
thelium and the stratum intermedium but a large amount 
of submucous tissue, composed of long branching fusiform 
connective tissue cells imbedded in a thin stroma, which also 
contains blood-vessels, and at times, tiny masses of epithelium 
( u Glands of Serres"). The latter are derived from the rem- 
nants of the fenestrations of the tooth band. The former 
seem to run right down to the condensed papillary tissue on 
the surface of the stellate reticulum, as if they were carrying 
special nutritive material to this region. 

In the young pulp, the walls of the blood-vessels and rudi- 
mentary myelinic nerve fibres make their appearance, the 
first by the approximation and joining up of the branching 
process of the longer cells, running singly in a line, the sec- 
ond by the development of the cells in longitudinal bundles. 

The vascularity or otherwise of the enamel organ is not yet 
determined, many competent authorities holding opposite 
opinions on this subject. Thus Lionel Beale, Leon Williams, 
Howes, and Paulton assert that a vascular network is to be 
found in the stratum intermedium, while Tomes, Paul, An- 
drews, Wedl, Sudduth, and Magitot affirm its non-vascularity. 

The author in a joint paper with H. W. Marett Tims has 
recently described the presence of blood-vessels, containing 
erythrocytes in the enamel organ of the Australian wallaby. 



262 DENTAL HISTOGENESIS 

("Tooth Germs in the Wallaby, Macropus billiardieri." Proc. 
Zoolog. Soc, London, 1911.) 

(x) The Blood Supply of the Developing Dental Tissues 

In determining the relationship which normally exists 
between the vascular supply of the dental tissues and the tis- 
sues themselves, it is necessary to consider the origin of the 
blood-vessels, their arrangement and mode of distribution, 
and the areas supplied by them. Where great development 
is taking place there is a free blood supply, and the more com- 
plex the organisation of a part — whether in anatomical struc- 
ture or location or in physiological function — the more abun- 
dant anastomosis of capillary blood-vessels is found. And 
this anastomosis is most important in controlling the growth 
of the tissue, as on it depends the hypertrophy, or atrophy, 
or normal conditions of the part. For should the blood stream 
be increased or accelerated, then overgrowth results; while, 
on the other hand, should it be diminished or occluded, it is 
followed by shrinkage, atrophy, degeneration, and death. 

Hence the blood supply of the hard and soft dental tissues 
is of vital importance; when normal, the tooth undergoes 
the changes consequent on evolution, and, finally, is erupted 
in a perfect condition; when abnormal, hypertrophies and 
atrophies of the whole or parts of the teeth are produced, 
and irregularities of external configuration, defects in quality 
of the organic and inorganic substances and other deviations 
from typical forms occur. 

The most useful subject for the purposes of the examination 
of the capillary arrangement is an injected section, in which 
the functional activity of development is most progressive, 
and most clearly discernible — a section whose genetic cells are 
most busily engaged in producing the various dental and 
peri-dental structures — a section, in short, which exhibits 
the birth of the life-history of a tooth. 

Here it is found that the tissues formed from each layer of 
the primitive blastoderm are supplied by separate sets of 
vessels. There is (i) an external or superficial, and (ii) an inter- 
nal or deep network, the former being distributed to the tissues 



development of teeth in Mammalia 263 

which are ectodermic in origin, including gum and certain parts 
of the enamel organ; the latter to those arising from the meso- 
derm, including dentine papilla, dental capsule and surround- 
ing bone. Thus, the external set of vessels is distinctly sepa- 
rated from, and has no connection with, the internal deeper 
set, except at one part, viz., the periodontal membrane, where 
they meet and anastomose freely (see Plate I). 




Fig. 229. — A portion of the blood supply of the stratum intermedium of the 
enamel organ of the section photographed in Fig. 227. Magnified 300 times. 
The staining was unsuited to reveal the structure of the ameloblasts; but it 
displays the erythrocytes which have been retained in situ. 

(i) The external set supplies the enamel organ and gum. 
On examination of the enamel organ proper, it is found that 
its external part is absolutely free from any closely meshed 
network of capillaries. The layer of cells, forming the ex- 
ternal epithelium and the thin branching cells of the stellate 
reticulum have no blood supply. One or two large non-branch- 
ing vessels traverse the space occupied by the reticulum, from 
the thick gum and connective tissues lying external to the 
enamel organ. These, having advanced as far as the stratum 
intermedium, suddenly break up into numbers of small capil- 



264 DENTAL HISTOGENESIS 

laries, and form a beautiful plexus which supplies the cells of 
this intermediate layer and the internal epithelium. 

But the capillaries are placed very closely together over 
the layer of ameloblasts — a fact explained by the activity and 
importance of these cells in the formation of enamel and their 
consequent necessity for a large supply of blood. 

Little need be said of the vessels of the gum. The stratum 
corneum, lucidum, and granulosum are non-vascularised: the 
rete Malpighii and fibrous connective tissue of the dermis 
differing greatly by being abundantly provided with numerous 
straight, long vessels which ramify in every direction. It is 
clear, therefore, that the nourishment of enamel organ and 
fibrous tissue of the gum emanates from the same source, and 
is quite differentiated from that of the other dental structures. 

(ii) The internal set supplies the dentine organ, dental capsule, 
and surrounding bone. 

In the dentine organ, the pulp has by far the largest and 
most important system of blood-vessels. Here, one large vessel 
enters at the apical foramen of the tooth, and occupying its 
longitudinal axis, passes sinuously outwards, to end near the 
newly formed dentine. As it proceeds, its calibre becomes 
somewhat diminished in size, and in a thick plexus of vessels 
its branches terminate beneath the odontoblasts, some run- 
ning, in adult pulps, into the basal layer of Weil. There appears 
to be no definite regularity in the arrangement of the primary 
branches: they leave the large arterial trunk at a considerable 
angle — in some sections this approaches to, even if it does not 
exceed, a right angle. The secondary and other branches have 
a similar arrangement. The greater number of the minor distal 
branches run parallel to the dentogenetic zone under cover of the 
odontoblasts, between and around which their ultimate ramifi- 
cations are distributed. These cells and the small round pulp 
cells which lie closely to them, have, therefore, an abundant 
supply of blood, brought about in a similar manner to that 
which obtains in the cells of the stratum intermedium, and inter- 
nal epithelium. 

The comparative size of these pulp vessels is much greater 
than that of the fine closely set capillaries of voluntary muscle 



development of teeth in Mammalia 265 

fibres; they bear a slight analogy to them, but none of the vari- 
cosities or spherical dilatations found on the walls of the latter 
are to be observed in the former. 

The advantages of this peculiar method of arrangement — 
the sinuous primary arterial trunk, the branches coming off 
at right angles, the minute anastomosis beneath the dentine — 
are manifest at once. It is evident that they are thus distrib- 
uted, first, to give as large an area of blood supply to the pulp 
tissues in as small a space as possible; and, second, to prevent 
shock or any other extraneous influence from acting injuriously 
on its delicate elements. In this manner, a flow of blood to the 
part is maintained — constant and uniform, two necessary 
factors in the production of perfect development, growth, and 
nourishment. 

There is no collateral circulation in the dental pulp. 

Included in the term "dental capsule" at this period of the 
genesis of the tooth, are its products, the cementum and perio- 
dontal membrane. 

It is difficult to determine absolutely whence and how the 
cementum is nourished. It would seem to come chiefly from 
the periosteal vessels. That trophic influences are exercised 
upon it to a certain but limited extent, is an undoubted fact, and 
it is equally certain that the dentine is not the medium by 
which they come. Hence it is fair to presume that the same 
vessels which supply the alveolo-dental membrane, vitalize 
the tissue by means of an exudation of lymph through their 
walls, which passes into it via the channels which contain 
Sharpey's perforating fibres. It may be assumed, however, 
that cementum is practically devoid of nutrition. 

Wedl 1 was the first to demonstrate that the dental perios- 
teum has three sources for its blood supply, viz. : (a) from the 
gum, (b) from the pulp, and (c) from the adjacent bone of the 
alveolar process. 

In regard to the first, it has already been shown that the 
external and internal sets unite in this situation, the vessels 
of the gum running downwards to anastomose with the 

1 "Pathologie der Zahne," 1870. 



2 66 DENTAL HISTOGENESIS 

internal set which supplies the dental capsule. But also loops 
of capillaries from the main arterial trunk of the pulp, before it 
enters that organ, can be seen spreading outwards and joining 
the before-mentioned vessels (see F, in Plate I). And in 
addition, numerous offshoots from the capillaries of the alveolar 
bone run towards the cementum, and form thick plexuses 
with the other two. The periosteum is, therefore, most richly 
vascularised, and forms by its method of attachment the 
vascular bridge, so to speak, between the living tissues of the 
jaw and the tissues of the tooth. 

The vascularisation of the bone of the alveolus calls for no 
further comment here, being identical with the blood supply 
of cancellous bone elsewhere. 

Briefly, to summarise, it can be said with tolerable cer- 
tainty that of the soft tissues, the pulp as being the most 
important nutritive agent, has the greatest, and the gum the 
smallest system of capillaries; while in the enamel organ the 
reticulate cells, and the external epithelium are destitute of 
any vessels whatsoever. 

An examination of the section from a photomicrograph of 
which Fig. 227 is reproduced, shows, however, that while blood- 
vessels do not actually anywhere pierce the stellate reticulum, 
yet long capillaries run freely everywhere immediately out- 
side the external epithelium; and where this is closely applied 
to the stratum intermedium (the intervening stellate tissue 
being atrophied), the numbers and size of the capillaries are 
greatly increased. This must not be interpreted, however, 
as signifying complete, but only as a modified form of vasculari- 
sation of the enamel organ. 

The cells of the internal epithelium must obtain a free 
blood supply from somewhere, for the purpose of manu- 
facturing the calcific basis of enamel, and it is difficult to con- 
ceive of this physiological phenomenon occurring as a product 
of cells which have no contiguity whatever with the vascular 
system of the body. 

An important addition to the literature of the vascular 
supply of the teeth of man comes from the pen of Dr. W. 
Lepkowski, of Cracow. Following up original work on in- 



development of teeth in Mammalia 267 

jected preparations of the teeth of the lower placental verte- 
brates, there appeared an interesting article on "The Distribu- 
tion of the Blood-vessels in the teeth of Man" in the "Anato- 
mische Hefte." 1 

"In a foetus of seven months the alveolar artery provides 
one branch for each tooth germ which is thus entered at its 
base. The artery directly before its entrance into the sac is 
still to be recognised as such, and can be easily distinguished 
from the veins accompanying it. Further on, the walls of 
the artery become so thin that even in stained preparations 
they can no longer be distinguished from the two veins ac- 
companying it. The vessel now rises to the highest part of 
the pulp and there divides into a number of branches, which 
spread out in a fan-like fashion from the base to the apex of 
the tooth germ. These branches are really capillaries. They 
proceed between the odontoblasts up to the dentine and there 
form broad loops which unite with each other. As has already 
been described in animals, there also spreads out in man, on 
the surface of the pulp between the odontoblasts, a broad net 
of capillaries, which is distinguished from the remaining woof 
running through the pulp by its breadth and density. An 
examination of numerous sections teaches one that the distribu- 
tion of this capillary net is not, however, the same on the whole 
surface of the pulp. At the base of the tooth the vascular 
anastomosis is always denser and more interwoven than to- 
wards its apex, where the net becomes comparatively broader 
and looser. This arrangement of the vessels follows the ar- 
rangement of the odontoblasts. With low magnifying power 
there can be seen, in preparations stained with carmine, a 
broad band of odontoblasts at the base of the tooth germ just 
where the vessels also are present in greater numbers; towards 
the top of the tooth germ the breadth of the odontoblast layer 
decreases appreciably, and simultaneously the network of the 
vessels becomes looser. It can scarcely be doubted that both 
appearances are connected with each other. It is also easily 
to be explained why at the base of the tooth germ the vessels 

1 "Die Verteilung der Gefasse in den Zahnen des Menschen," Weisbaden, 1901. 



268 DENTAL HISTOGENESIS 

and odontoblasts are more closely arranged than elsewhere; 
for it is on the base of the tooth that new substance is deposited, 
and the vessels and odontoblasts (sic) are chiefly concerned in 
this process. As this distribution of the vessels and cells can be 
seen in every preparation, we may consider this kind of arrange- 
ment as the rule in the formation of teeth. In reference to the 
mutual relationship between capillaries and odontoblasts, it 
may be mentioned that the former, as loops, reach, between the 
odontoblasts, up to the dentine layer. They take no direct 
share in the formation of the dentinal tubes. On the other hand, 
we must assume that they convey the necessary material for 
the building up of the tooth and induce special activity of the 
odontoblasts. The dense distribution of the vessels at the 
surface of the pulp, between the odontoblasts generally, as 
also specially at the basal parts of the tooth germ, points to this. 

"If we compare the vascular systems in the various teeth 
of the same embryo, we obtain deviations according to the 

number of the roots and the form of the tooth crown 

If we take a section through a single root tooth germ — for 
example, a canine — we get, in the centre of the pulp, a bundle of 
vessels, which after their sub-division into finer ramifications 
provide for the entire pulp, and under the dentine spread out 
in a characteristic manner. In the germ of a two-cusp tooth 
there are present two bundles of vessels separated from each 
other. From this we get the impression that the tooth had 
been developed from a number of single teeth corresponding 
to the cusps and roots. A series of sections obtained from the 
tooth germ of a three-rooted molar favours the proposition still 
more. We see, therefore, in the first sections two bundles of 
vessels and two cusps. The vascular bundles enter separately 
at the base of the tooth germ, and only in their ramifications 
in the tooth pulp do they become connected with each other." 

As a carollary to this line of argument this author formulates 
the following highly interesting theory: "I believe that my 
results on the distribution of the vessels in developing molars 
speak in favour of the hypothesis advanced by various inves- 
tigators, among them Dybowski and Rose ('Ergebnisse der 
Anat. und Entwickelungsgeschichte,' 1899), that the het- 



development of teeth in Mammalia 269 

erodont set of teeth of man and mammals has originated from a 
homodont dental apparatus. The individual cone-shaped teeth 
such as exist to-day in reptiles, becoming approximated through 
the shortening of the maxilla, fuse, so to speak, and form com- 
pound teeth, which according to their function and the devel- 
opment of the osseous parts surrounding them, in the course 
of time, receive their present shape. The witness for their 
descent from simple teeth is to be sought for in the rudiments 
of several cusps, and their separate vascular supply during 
their development. Not much reliance must be placed upon 
the number of roots with which they are provided. As already 
stated, this is as a rule reduced, perhaps in consequence of 
mechanical influences. Besides, as is known, there are often 
found four, five, or even six roots on molars. Their presence 
proves that corresponding to the number of cusps under fav- 
ourable conditions they may continue to exist in their original 
type without reduction, of course, as rudiments, of the former 
homodont masticating apparatus. 

"The vessels which externally surround the enamel organ 
are connected with the pulp-vessels. The vessels originate in 
the inter-alveolar arteries which supply the cancellous bone 
substance of the maxillae. They spread out in a dense woof 
at the surface of the enamel organ, but do not, however, 
penetrate between the ameloblasts of the enamel organ. 
To judge from microscopical sections they belong to the 
venous system. They surround the tooth germ from the 
first rudiments of its development. Notwithstanding that they 
deviate from the method of arrangement of the pulp-vessels, 
they agree with the latter in so far, in a physiological sense, 
that they play an active part in the formation of the enamel, as 
the others have an active share in the formation of dentine. 
On thorough examination of the preparations, it is observed 
that at the apices of the tooth-germs where the enamel is thick- 
est, the vascular net is also denser. The points correspond to 
the highest parts of the tooth. When the tooth crown is near 
its completion, the activity of the enamel cells gradually ceases, 
and the vessels supplying them slowly undergo retrogressive 
changes. Within the tooth, however, the formative activity 



270 DENTAL HISTOGENESIS 

of the odontoblasts and the blood-vessels still continues, until 
the dentine of the crown and the roots has been built up. 

"The disappearance of the vessels of the enamel organ 
begins at the summit of the tooth, and proceeds in the direction 
of the root. In the stages of evolution, in which the tooth is 
erupted, the superficial vessels unite with those of the gum; 
those lying deeper surround the root and supply its newly 
formed periodontal membrane. They spread out on the walls 
of the alveolus, and remain in this position, as long as the 
tooth exists. ... Of the pulp-vessels, individual vessels or 
also bundles of them occasionally separate, perforate in places 
the dentine-layer and the enamel-layer and obtain connection 
with vessels surrounding the tooth germ on the outside. Ex- 
amples of such vascular connections I have observed in tooth 
preparations of the embryos of the lower animals, as also in 
those of man. 

"On examining such sections one might be tempted to 
think of an analogy with the Haversian canals in bones. How- 
ever, the vascular connections of the kind mentioned are too 
rare to be looked upon as quite normal formations. I believe 
I can explain in another way this vascular communication 
which arises but rarely. 

"In later stages of development, and in adult man, one 
finds at the lateral surfaces of the teeth, and more especially 
on the molars, a funnel-shaped constriction. In sections, 
made transversely through the tooth at the level of such a 
depression, one observes the dentine tubes markedly condensed, 
as it were, as if there were present a scar in the dentinal tissue, 
which reached up to the pulp cavity. 

"In my opinion these cicatricial formations in the developed 
tooth are related to the vascular communications just de- 
scribed. I myself, during my researches on fully formed teeth 
have never seen any other formations than this cicatricial 
contraction, but Thiel mentions a case which tells in favour 
of my view. Scheff cites the same case in his 'Handbuch' 
when discussing haemorrhage after extractions. After the 
extraction of the first upper premolar on the right side, con- 
siderable bleeding followed, which, on careful examination, 



development OF teeth in Mammalia 271 

was traced, from the wall of the alveolus, to a bundle of vessels 
which entered the tooth at the neck and ran transversely 
through the dentine up to the pulp. At the outset it is not to 
be assumed that the vessels in the case mentioned above 
originally perforated the fully formed tooth, because the tooth 
substance in advanced life is too hard to allow blood-vessels to 
penetrate, and, on the other hand, the vascular supply at that 
period, in comparison with that of a younger age, is too slight." 

Lepkowski holds that: "If we compare the vascular dis- 
tribution in the teeth of man with that of mammals, such as the 
pig, the horse, and the rabbit, we find, what was to be expected, 
that there are no appreciable differences. The course of the 
vessels, their distribution, the density of the vascular net at 
corresponding places, and its relationship to the tissues in 
course of formation, are the same here as there. The more 
pronounced differences are in the number of the vessels in the 
tooth germ. In embryos of the animal species cited, there 
exists in the pulp, as also specially in the enamel organ, far 
richer vascular ramifications than in the corresponding teeth of 
human embryos. The explanation, to my idea, is not far to 
seek. There exist very considerable differences, first, in the 
relative size of individual teeth between animals and man 
(for example, the canine); and secondly, in the thickness of 
the layers of substance. In the dog the thickness of the 
enamel layer surpasses by far that of the human teeth. It 
is, therefore, quite natural that the tooth germs of animals 
are provided more richly with vessels. 

"Otherwise the vascular distribution from embryological 
periods up to the complete development of the teeth is, in 
its fundamental characteristics, analogous in man and ani- 
mals. The observations also which I have made in regard 
to the relationship of vessels to the cusps and roots in human 
teeth may be similarly applied to the teeth of animals." 

The subject is one of importance, and invites greater 
attention than has hitherto been accorded to it. It should 
not, however, be so difficult a matter to determine in these 
latter days; since the modern introduction into the methods 
of Dental Microscopy, of solutions of formic aldehyde, as a 



272 DENTAL HISTOGENESIS 

fixing and hardening agent, has shown that the natural in- 
jection of blood-vessels by blood cells can be maintained almost 
exactly as during life. 

(xi) Final Stages of Evolution 

Later phases in the evolution of the teeth include the 
growth of enamel and dentine, the approximation, to the sur- 
face of enamel, of the external epithelium as the cellular layer 
of Nasmyth's membrane, and the complete organization of 
the dental capsule. 

(xii) Dental Capsule 

As a thick investing fibrous belt this structure envelopes 
the whole of the tooth, except at the apex of its root. Each 
tooth has its own capsule: and each capsule has a separate 
entity. At first consisting, as has already been pointed out, of 
layers of flat fusiform cells, round cells begin to be formed 
within it. These move in an inward direction, and assume 
the shape and functions of ordinary osteoblasts. The result 
of their activity is to deposit cemental matrix, which, about 
the times of the completion of the crowns of the teeth, becomes 
intimately and securely applied to the external periphery 
of the dentine. These cells probably pour it out as a homo- 
geneous ossifying flood. 

The remainder of the capsule becomes, almost synchronously, 
transformed into the periodontal membrane. 

It is likely that a special cement organ, which according to 
Magitot partakes of the nature of fibro-cartilage, exists over 
the crowns of the developing teeth of the ruminating groups 
in Artiodactyla. A cement organ, as such, has no existence, 
however, in the teeth of man. 

An examination of the tooth band of the permanent tooth, 
in Figs. 231 and 232, would lead one to suppose that here was 
a truly remarkable example of four successive tooth germs 
in man, viz.: pre-milk, deciduous, permanent and post-per- 
manent (V u E, and DP, PZ, and V 2 ). Some authors, in- 



development of teeth in Mammalia 273 




Fig. 230. — To show the vascular supply ot the dentine papilla. Magnified 
55 times. 



274 



DENTAL HISTOGENESIS 




Fig. 231. — Coronal section through the mandible of a human foetus, at about 
the 170th day of intra-uterine life. Prepared by decalcification, after fixing in 
formic aldehyde. Stained with hsematoxylene, and counterstained with eosine. 
Magnified 15 times, e. Enamel of deciduous tooth; d. Dentine; s.r. Stellate 
reticulum; d.p. Dentine papilla; d.c. Dental capsule; p.z. Tooth band of permanent 
molar tooth on lingual side; b.v. Blood-vessels extending to external epithelium; 
g. Oral epithelium; b. Bone of jaw; m.n. Mandibular nerve; Vi. A supposed vestig- 
ial germ (pre-milk) ; V2. A supposed vestigial germ (post-permanent). 



development of teeth in Mammalia 275. 




Fig. 232. — The same as the preceding. To show the "tufts" on the tooth 
band of the permanent germ. Magnified 75 times, p.z. Tooth band of 
permanent tooth germ; t. "Tufts;" Vi. Part of the tooth band which might be 
considered by some authorities to represent the tooth band of a vestigial (pre- 
milk) tooth; v?. That of post-permanent tooth; b. Blood-vessels. 



276 



DENTAL HISTOGENESIS 




M N 
Fig. 233. — Sagittal section of mandible of kitten, with the deciduous and 
permanent teeth in situ. The former is fully erupted. Prepared by decalci- 
fication after fixing in formic aldehyde, and hardening in alcohol. Magnified 
15 times. Represents the stage of development in man about the 18th month 
after birth, d.t. Dentine of deciduous tooth; p. Its pulp; p.m. Blood-vessel in 
its root membrane; ao, Its absorbent organ; d. Dentine of permanent tooth; 
d.p. Dentine papilla of same; b. Bone of jaw; c. Gum tissue; m.nt. Mandibular 
nerve. 



development OF teeth in Mammalia 



277 



eluding Rose, Leche, Kukenthal, etc., would accept the off- 
shoots, as these aberrant tooth bands. As Tomes, however, 




Fig. 234. — The permanent tooth germ of preceding figure. Magnified 65 
times, d.p. Dentine papilla; o. Odontoblasts; d. Dentine; e. Enamel; a. Amelo- 
blasts; s.r. Stellate reticulum; e.e. External epithelium; d.c. Dental capsule; 
b.v. Blood-vessels going down to external epithelium; d.t. Dentine of deciduous 
tooth; A.o. Absorbent organ of deciduous tooth; b. Bone of the jaw; m.a. Man- 
dibular artery; m.n. Mandibular nerve. 



points out (op. cit. p. 352), scepticism can only be removed when 
these structures have become differentiated into external and 
internal epithelia, and calcification is seen to be commencing. 



278 DENTAL HISTOGENESIS 

(xiii) Recapitulation 

It seems advisable, for the simplification of a somewhat 
abstruse subject, such as the Development of teeth in Mam- 
malia, to here append a brief outline of the histories of the 
various structures met with during such a study. 

1. Epithelial Inflection. — Due to individual proliferation of 
deepest layers of cells of the oral epithelium, and collective 
penetration into the sub-lying tissues: undergoes cleavage 
longitudinally; thus forms (i) Labio-dental strand and (ii) 
tooth band, Fig. 201. 

2. Dental Furrow. — A slight superficial indentation over the 
epithelial inflection. 

3. Labio-dental Strand, or Lip Furrow. — Outer division 
of primary epithelial inflection after its cleavage: elongates in 
vertical direction; widens; central cells atrophy; thus pro- 
ducing open sulcus between lips or cheeks and teeth and al- 
veolar processes of jaws, Fig. 203. 

4. Tooth Band, or Common Dental Germ. — Inner division 
of primary epithelial inflection, after its cleavage: elongates: 
has (i) as one portion, on labial side, depression which goes 
to form enamel organs of ten deciduous teeth; and as another 
portion (ii) free end or border on lingual side, which, continuing 
to grow, produces enamel organs of ten permanent teeth on 
lingual side of deciduous germs; and still growing, extends 
backwards to form enamel organs of first, second and third 
permanent molars; is continuous around whole length of jaw: 
degenerates and becomes cribriform; finally disappears, leaving 
sometimes small epithelial remnants in situ, known as "glands" 
of Serres, also epithelial bodies in dental capsule, supernumerary 
teeth, true gemination, enamel nodules, etc. 

5. Enamel Organ. — Formed by expansion of base of tooth 
band: ectodermic in origin; assumes various shapes; consists of 
external epithelium, stellate reticulum, stratum intermedium 
and internal epithelium; disappears after alveolar crypts are 
completed. 

6. Neck of Enamel Organ. — Attenuated form of original 
tooth band: atrophies. 



development of teeth in Mammalia 



279 



7. External Epithelium of Enamel Organ. — Peripheral layer 
of round cells continuous with rete Malpighii on one hand and 
internal epithelium on other: undergoes modification and 
probably forms cellular layer of Nasmyth's membrane. 

8. Stellate Reticulum. — Ectodermic in origin: derived from 
central cells of tooth band; acts probably as "packing material" 
or filter; consists of large stellar cells with prominent nuclei, 
and long branching processes; nuclei atrophy and network 
entirely vanishes. 



% 




•Q 



/^ "'" /Tv( 



EO DP 




Fig. 235. 



Fig. 236. 



Fig. 237. 



Figs. 235, 236, 237. — Diagrams to show the tooth band, method of evolu- 
tion of the tooth germs of the deciduous teeth, and continuation of the tooth band 
to form enamel organs of their permanent successors, o.e. Oral epithelium; 
t.b. Tooth band in section; z. Tooth band seen sideways as a continuous sheet ; 
e.o. Enamel organs; d.p. Dentine germs of deciduous teeth; z.p. Continuation of 
tooth band going shortly to form enamel organ of permanent tooth germ on 
lingual side of the others. (After Stohr.) 



9. Stratum Intermedium. — Layer of round or polygonal cells 
intervening between last-named tissue and internal epithelium, 
from which it is separated, according to Leon Williams, by outer 
ameloblastic membrane: disappears. 

10. Internal Epithelium. — Continuous at edges with external 
epithelium; forms enamel-depositing cells or ameloblasts; 
thickest over cusps of teeth through individual cells being 
longest in these situations: as such disappears after enamel cal- 
cification is completed, but most probably persists in modified 
form as translucent pellicle of Nasmyth's membrane. 

11. Epithelial Sheath of Hertwig. — Continuation downwards 
to base of dentine germ of layer of internal epithelium: is 



280 DENTAL HISTOGENESIS 

believed to determine shapes of future roots; disappears; may 
leave unatrophied remnants as epithelial "rests" in periodontal 
membrane. 

12. Dentine Papilla. — Formed by upgrowth of mesoderm in 
concavity of enamel organ: mesodermic in origin; assumes form 
of future tooth, viz., conical, premolariform, molariform, etc.; 
persists as dental pulp. 

13. Dentogenetic Zone. — Band of formed but uncalcified den- 
tine, bounded externally by fully completed tissue, internally by 
layer of odontoblasts: disappears when work of calcification is 
done. 

14. Membrana Eboris or Odontoblasts. — Cylindrical bipolar 
cells situated at periphery of dentine organ and dental pulp; 
bounded externally by dentine, internally by basal layer of 
Weil: perpetually persist. 

15. Dental Capsule or Follicle. — Connective tissue capsule 
investing each tooth germ: mesodermic in origin, whence are 
derived periodontal membrane and cementum; persists till near 
time of eruption, then atrophies. 

FORMATION OF THE HARD TISSUES 

The study of the phenomena of the calcification of bone and 
other allied tissues involves the discussion of several subjects, 
such as chemistry, physics, physiology, as well as histology. 
It is obvious that the history of the embryology of the teeth 
would be incomplete if a record as to the modes by which osse- 
ous matter is deposited in the soft formative organs were 
omitted. 

The histological aspects of such a study can alone be included 
in a work of this character: for the principles of calcification 
generally readers are referred to the well-known writings of 
Tomes, Sims Woodhead, etc. 



DEVELOPMENT OF THE ENAMEL 

Sir John Tomes and his son, Andrews, Leon Williams, and 
others have paid much attention to investigating this difficult 



development of teeth in Mammalia 281 

question: and it may be repeated here that the absolute truth of 
the matter is unknown: but the balance of favour rests with 
those who hold the secretion theory. 

The following are brief outlines of various theories: — 
Sir John Tomes considered that the enamel is formed by 
conversion of the ameloblasts. The pronounced extremities 
of these cells undergo, first of all, certain chemical changes; 
later on calcification ensues. The central portions of the cyto- 
plasm of the cells calcify later than the peripheral: contiguous 
cells become united as calcification proceeds. 





Fig. 238. Fig. 239. 

Fig. 238. — Ameloblasts, with Tomes' processes. 



{Afte 



Fig. 240 
John Tomes ) 



Fig. 239. — Ameloblasts, two of which have been immersed in glycerine, and 
present trumpet-shaped ends towards the enamel. {After Tomes.) 

Fig. 240. — Ameloblasts, showing globular bodies. Tomes' processes, and the 
spongioplasm of the cells. (After Tomes.) 



Charles Tomes, in his recent researches on the development 
of enamel in marsupials, is led to the following conclusions: — 
(i) The ameloblast itself does not become calcified. 
(ii) The chemical and calcareous changes take place in or 
around a fibrillar process (Tomes' process), which, being 
continuous with the cytoplasm of the ameloblast, serves 
for the entire length of an enamel rod, and solidifies 
equally throughout in the enamel of man and all animals 
but marsupials and certain others (see p. 96). 
(iii) A tubular condition of the enamel rods is probably 
merely a stage through which all rods pass during their 
histogenesis. 



282 



DEXTAL HISTOGENESIS 



Graf Spee 1 was the first to notice and describe globular masses 
of some kind of calcareous material enclosed in the spongio- 
plasm of the ameloblasts. 

Kolliker (op. cit. p. 306) conjectured that enamel rods are 
produced by a secretion by the cells of the enamel membrane 
which penetrates the membrana preformativa in a fluid condition, 
but hardens and ossifies- beneath it. 



ti 




Fig. 241. 



Fig. 



Fig. 243. 




Fig. 244. 



{After 
{After 



Fig. 241. — Ameloblasts prior to the start of formation of the enamel. 
Walkhoff.) 

Fig. 242. — The same, with commencement of formation of the enamel. 
Walkhoff.) 
Fig. 243. — An ameloblast. {After Waldeyer.) 

Fig. 244. — Isolated ameloblasts. H. Homogeneous mass of calcined material, 
extended from the cell through (c) the enamel membrane by dialysis, t.p. 
Tomes' processes. {After von Ebner.) 



Andrews has shown (Trans. World's Columbian Dental 
Congress, vol. I., 1893) that there is a deposition of droplets or 
spherules of calcoglobulin formed in the ameloblast, and that 
these are excreted by these cells at their dentinal ends to 
build up the enamel rods. The "fibres of Andrews" act as 
a sort of reticulum or scaffolding to determine the arrange- 
ment of the deposition; the existence of these fibres being 
ultimately blotted out by the dense calcification of the tissue. 

G. Arnell in u Zur Kenntniss der Zahnbildenden Gewebe" in 
Retzius' "Biologische Untersuchungen herausg.," II., dem- 
onstrated, as long ago as 1882, that the inner ends of the 

'"Ueber die ersten Vorgange der Ablagerung des Zahnschmelzes." — Anat. 

Anzeig., 1887. 



development of teeth IN Mammalia 



283 



ameloblasts are directly concerned with the formation of the 
enamel rods, a finely granular deposit occurring round these 
ends. 




Fig. 245. — Section of developing tooth of a calf, at the commencement of 
enamel formation. Magnified 1,000 times. It is clearly seen that the organic 
substructure of enamel and dentine is formed from the cytoplasm of the cells. 
a. Cytoplasmic network in ameloblast; b. c. d. e. Globular or spherical patterns 
of cytoplasm. Radiating lines are seen to pass from a central mass to a rim 
which bounds the circumference, thus resembling nuclear structure. A like 
appearance is shown in the completely formed enamel rods. f. Shows the 
cytoplasm of an ameloblast passing without break of continuity into the forming 
enamel. (Photomicrograph by Leon Williams.) 



Heitzmann and Bodecker consider that the ameloblasts 
"break up" into "embryonal corpuscles," which afterwards 
become calcified. 



284 



DENTAL HISTOGENESIS 



Xavier Sudduth thinks that the ameloblasts excrete the 
enamel. He is more concerned with the problem whence 
they get their nutritive supply, and suggests that the calcium 
salts are stored up in the meshes of the stellate reticulum of 
the enamel organ, which thus furnish material for the first 
formed layer of enamel. 




Fig. 246. — Section of mature human enamel of fine quality. Magnified 
3,000 times, a.b. Calcified cytoplasmic network composed of very fine granular 
threads of fibres; c.d. Enamel rods built up of sectional or globular arrangement 
of calcified cytoplasm. Radiating granular threads pass from a central mass 
to the border of the sectional part of the rod. (Photomicrograph by Leon 
Williams.) 

After this is laid down, the enamel organ having disappeared 
from over this calcified layer, a further supply of calcium salts- 
is provided by a rich plexus of capillaries which is found in 
direct communication with the ameloblasts. 



development of teeth in Mammalia 285 

Leon Williams holds views on somewhat similar lines. 
According to him, the stratum intermedium absorbs from the 
capillaries an albumen-like substance. This is ingested by the 
ameloblasts, which transform it into enamel globules, and so 
form the rods. Globules are successively produced within the 
ameloblasts. 




Fig. 247. — Section of mature enamel, showing calcined cytoplasmic network 
at a. b. and c. Magnified 1,500 times. Compare Fig. 245. {Photomicrograph 
by Leon Williams.) 



"The cytoplasm," he writes, "of the ameloblasts has a 
fairly uniform structure, which consists of a number of globular 
masses of spongioplasm of the same diameter as the cell, and 
united longitudinally by somewhat coarser plasm-strings — 
'the fibres of Andrews.'" "There are many indications that 
these enamel globules are formed by the nucleus of the amelo- 



2»0 DENTAL HISTOGENESIS 

blast; and they appear to pass down the cell by the natural proc- 
ess of growth, as new ones are formed above, to be finally 
shed off the inner ends of the cells on to the surface of the form- 
ing enamel, where they become completely infiltrated with the 
albumenoid lime-conveying substance, and calcified. Enamel 
globules are of uniform size, and quite distinct from the 
more transparent and irregularly sized masses of calco- 
globulin." "Enamel rods are manufactured by successive, 
rhythmical, orderly deposits of these enamel globules, the 
calcoglobular masses fusing and forming the interprismatic 
substance." 

He finally further adds (The Dental Cosmos, p. 477, June, 
1896): — "There are two distinct products of the enamel- 
forming organ. One of these products, from which the enamel 
rods are built up, is formed by the ameloblasts, and is probably 
a direct nuclear formation. In the enamel cells it takes the 
shape of globular bodies containing granules, sometimes 
arranged with more or less order, so as to resemble the nucleus of 
the cell. In the formed enamel rod these globular bodies are, 
more or less, compressed into disc-like shapes, and are sometimes 
nearly, or quite, melted into one another. Simultaneously 
or alternately with the deposit of the globular bodies, a trans- 
lucent albumen-like appearing substance is seen passing out 
of the ameloblasts. This substance is probably taken from the 
blood by the secreting cells of the stratum intermedium, and 
evidently contains the mineral matter of which the com- 
pleted enamel consists. As the globular bodies pass from 
the ameloblasts they are seen to be connected by plasmic 
strings, which strings can often be plainly seen in the body of 
the ameloblasts. The globular bodies are often connected 
laterally by strings or projecting processes. Around the 
skeleton thus formed, which constitutes the real structure of 
enamel, the albumen-like substance flows, supplying the 
cement substance, and probably the mineral matter for the 
calcification of the whole. All of this structure can be plainly 
seen in mature enamel; but in normal enamel it is every- 
where completely calcified, and contains no trace of organic 
matter." 



development of teeth in Mammalia 287 

To sum up: The theories may be classified under three dis- 
tinct headings: — 

(1) Enamel rods are produced by conversion or trans- 
formation in situ of the ameloblasts (John Tomes, 
Waldeyer, Kolliker, &c). 

(2) Enamel rods are produced by excretion or secretion, 
from the ameloblasts (Charles Tomes, Leon Wil- 
liams, Sudduth, Andrews, Schafer, &c). 

(3) Enamel rods are produced by growth of the amelo- 
blasts at the end next to the formed enamel, and the 
new growth in the younger part is calcified as soon as 
it is formed (Schwann). 

The established facts that require no controversy about this 
intricate matter are quite clear, and seem to be that the layer 
of formed but uncalcified developing enamel is outside the 
main body of the ameloblasts; that it has Tomes' processes 
penetrating it at regular intervals; that it is produced pari 
passu with the first layer of uncalcified dentine against which 
it is applied; that it is at first formed and afterwards calcified; 
that it stains deeply with osmic acid; and that it chemically 
resembles keratin, inasmuch as it offers great resistance to 
destruction by any of the mineral acids. 

DEVELOPMENT OF THE DENTINE 

Researches as to the methods of formation, calcification, 
and the growth of dentine are not so beset with the innumerable 
difficulties attending like investigations with regard to the 
enamel. Though the first genesis of this tissue occurs at a 
period of time slightly antecedent to that of enamel, the fact 
of its continuance after the disappearance of the enamel organ 
is completed, and the part it plays in the production of the 
roots of teeth, with or without persistently growing pulps, 
as a physiological process, make investigation easier. It must 
likewise be remembered that certain pathological conditions 
of the pulp (q.v.) in which calcareous (dentinal) masses are 
developed — pulp nodules, adventitious dentine, etc. — are of 
fairly common occurrence. Added to this, also, must be the 



205 DENTAL HISTOGENESIS 

fact that opportunities sometimes arise of observing the manner 
of growth of dentine in odontomes, where the fibrous tissue 
capsule is still in normal anatomical relationship with the hard 
parts (see Chapter XV, Vol. II). 

Hence it follows that recent discoveries have a tendency 
to prove the fallaciousness of the tenets maintained by Waldeyer 
in 1870, and also held by Boll, Beale and others, and that, in a 




Fig. 248. — To show the process of calcification of human dentine. Regularly 
arranged tubules traverse the matrix, the sheaths of Neumann being indistinct, 
till they cross one of the calcospherites in which calcium salts are being deposited. 
Here they appear as black lines. From a section in the possession of A. W. W. 
Baker, of a tooth erupted at birth. 

word, dentine formation proceeds on somewhat similar lines 
to those which obtain in intra-membranous ossification of bone. 
These lines are not quite identical, inasmuch as the so-called 
odontoblast cells possess persistent processes, and do not be- 
come encapsuled as is the fashion with osteoblasts. 

Since 1889 the author has never held the view, which had 
been originally formulated by Waldeyer, 1 that odontoblasts 

1 "Human and Comparative Histology," Strieker's "Handbook;" Sydenham, 
Soc., Vol. I., p. 463, 1870. 



development of teeth in Mammalia 289 

form matrix, sheath of Neumann, and dentinal fibril; and 
Howard Mummery following up and amplifying the work of 
von Ebner in tracing throughout the pulp a fine connective 
tissue stroma which is continuous with that in the dentine 
matrix, has unconsciously, perhaps, but none the less certainly, 
corroborated this hypothesis. 

Thus there is now established, with a probably great degree 
of accuracy, the opinion that dentine is a product of certain 
round cells of the pulp of an osteoblastic nature, whose func- 
tion it is to abstract lime salts or carbon dioxide, from the 
vessels of the pulp and lay down matrix as a continuous sheet 
of formed material on the periphery of that organ. This is 
found in the teeth of man, as well as fish (vaso-dentines). 

Howard Mummery's paper, Philosop. Trans. Royal Soc. of 
London, Vol. 182, pp. 527-545, entitled "Some Points in the 
Structure and Development of Dentine," should be perused 
by all interested in the matter. Here it need only be said that 
his summaries point to the opinions that: — ■ 

(i) The mode of development of hard dentine presents a 
strong analogy to the development of bone in 
membrane, 
(ii) In human dentine trabeculae are seen shooting inwards 
into the pulp from the surface of the forming dentine; 
these trabeculae sometimes exhibiting "an appearance 
as if stiffened by the deposit of lime salts in advance 
of the general line of calcification," and being continu- 
ous with the connective tissue fibres of the pulp, 
(iii) The fibres and trabeculae are covered with cells which 
in many parts thickly clothe them, and have similar 
functions to osteoblasts. "Smaller cells are inti- 
mately associated with the odontoblasts proper, the 
latter cells being also involved in the connective 
tissue stroma in continuity with the dentine, and, ac- 
cording to the view which, under the circumstances, 
seems most reasonable, these cells together secrete a 
material which calcifies along the lines of the odonto- 
genic fibres" (see Figs. 36, 37, 38, 39, 40 and 41). 



29O DENTAL HISTOGENESIS 

Since 1892, when the above was written, Howard Mummery 
has changed his opinion. In 1913 he contributed to the Phil- 
osoph. Trans. Roy. Soc. a paper entitled "On the Process of 
Calcification in Enamel and Dentine," and his new views are 
based on the assumption of the innervation of the dentine. He 
does not consider that sensations are transmitted through the 
dentinal fibrils, and writes as follows: 

"The evidences that the odontoblast cells are the principal 
active agents in calcification of the dentine are, I venture to 
think, quite as conclusive as the similar evidences of the func- 
tion of the ameloblasts — a function which has not yet been 
doubted in their case. 

"As nerve-fibres traverse the dentinal canals, the fibril cannot 
be looked upon as a transmitter of nervous impulses — the cells 
have granular contents, they lie in a rich plexus of blood-vessels, 
and we know that active secretion is associated with an in- 
creased blood supply; like other secreting cells, they are large 
and well differentiated from the surrounding tissue elements, 
and they retain their full size and characteristics during the 
actual deposition of the dentine in healthy teeth. 

"The protoplasmic prolongation of the cell in the form of the 
dentinal fibril would be considered to share in the functions of 
the cell of which it forms a part, and there are strong evidences 
that calcific matter is transmitted by the fibril. The trans- 
lucent zone in caries, which a great weight of evidence suggests 
is due to calcification in the tubes, and the peripheral occlusion 
of the tubes on exposed surfaces, point to this extension of the 
cell protoplasm being the channel by which lime salts are 
conveyed to the dentine. 

"If I am right in supposing that the sheath of Neumann 
serves as a dialysing membrane, the comprehension of the proc- 
ess of calcification in the dentine is somewhat simplified. The 
odontoblast cell, either alone or in common with other cells in 
the pulp which send processes to the dentine, would deposit 
the gelatinous basis substance in which calcification takes place 
— the substance which forms the odontogenetic zone — the lime 
salts taken up from the circulating blood by the secreting cells 
would be transmitted by the fibril, and passing by dialysis into 



development of teeth in Mammalia 291 

the matrix, lay down the calcifying material in the globular 
form, slow diffusion of the component salts, such as takes place 
through dialysing membranes, being an important factor in the 
production of the calcospherites." 



THE GROWTH OF THE DENTINE IN THE RABBIT AND CAT 

The following is a precis of Aitchison Robertson's experi- 
ments and observations on the growth of dentine in the per- 
manently growing incisors and also in the canine teeth of rab- 
bits and cats. They were undertaken to determine whether this 
tissue increased in size by interstitial growth or not; and the 
subjoined Tables of measurements and their summaries are 
exceedingly instructive (see Trans. Roy. Soc. Edinburgh, Vol. 
xxxvi) . 



METHOD OF INVESTIGATION 

"For the purposes of this inquiry the lower incisor teeth of 
the rabbit were chosen, for these teeth grow from persistent 
pulps and are therefore never shed. To observe their condi- 
tion at different stages of growth they were examined in (1) a 
rabbit newly born; (2) in a rabbit one month old; and (3) in 
an adult animal. These teeth, while still in situ in the lower 
jaw, were decalcified and sections made in an antero-posterior 
direction parallel to their long axes. The sections from the 
very centre of each tooth were alone used for measurement, 
as they contained the largest pulp cavity and went directly 
through the centre of the crown. These teeth, as they are 
worn down in front, are always being added to from behind 
and thus pushed forwards. The enamel is only found on the 
anterior and lateral surfaces, and is always thickest in the former 
position, where also the dentine is harder. Consequently, 
as the crown of the tooth is worn down, the anterior part, 
being harder, is not worn so fast, and thus the tooth becomes 
chisel-shaped. 



292 DENTAL HISTOGENESIS 

Measurements of Lower Incisor Teeth in Rabbits 



Newly born 



One month old 



Total length of tooth 
Greatest length of 

pulp cavity 

Greatest breadth of 

pulp cavity . . . 
Thickness of dentine 
I at middle of tooth. 
Greatest thickness of 

dentine at crown. .1 
Diameter of dentinal 

tubules at origin. . . |ji< 
Width of intertubu- 

lar dentine 

Character of denti-j 

nal tubules 1 Run obliquely in , Wavy course; not Wavy course; many 

straight lines; no branched. branches. 

\ branches; slightly 
wider near origin. 



\i inch 0.2 


3-2" inch .5 




j\i inch 1 . 12 


y& inch 0.17 


■%o inch 0.43 




1 inch 1 .0 


}io inch 0.033 


3-2 5 inch 0.04 




Yn inch 0.073 


H58 inch 0.0063 


3^2 inch .024 




1 H50 inch 0.044 


34s inch 0.02 


H2 inch 0.08 




% inch 0.12 


4000 inch 0.0000416 


/•24000 inch 0.0000416 3-24000 inch 0.0000416 


8000 inch .000125 


Via 00 inch .000 


[65 


3-6ooo inch 0.00016s 



The results of this table may be summarized as follows: — 

1. The fact of the great increase in length of the tooth is 
evident, it being six times longer in the adult than in the newly 
born rabbit. 

2. The pulp cavity increases in length in the same proportion. 

3. The width of the pulp cavity increases in a progressive 
manner. 

4. The thickness of dentine at the middle of the tooth and 
also at the crown increases nearly six times. 

5. The diameter of the dentinal tubules at the proximal end 
remains the same at each stage of growth. They are all slightly 
larger at their origin and diminish in calibre very gradually 
as they are traced outwards. 

6. The dentinal tubules become gradually more wavy in 
their course, and their lateral branches become evident in 
the adult tooth. 

"The odontoblasts form a complete lining to the inner sur- 
face of the dentine, and thus form, as it were, a bag enclosing 
the pulp and having its mouth at the inlet of the pulp cavity. 
Dr. Haycraft suggested that the ring of odontoblasts which 
forms the mouth of this bag might fitly be called the 'forma- 
tive ring,' because it is apparently here that new dentine is 



development of teeth in Mammalia 293 

constantly being formed. The new dentine pushes upwards 
that previously formed, which carries with it the odontoblasts 
attached to its inner surface by the dentinal fibrils. The 
odontoblasts which once composed the 'formative ring' are 
therefore carried up by the rising dentine, for as soon as each 
has deposited a little dentine at the extreme base of the tooth, 
it becomes fixed as a permanent odontoblast and is after- 
wards lifted up. Fresh cells are continually growing below 
those engaged in the production of dentine, and thus the exist- 
ence of the 'formative ring' is continued. From whence 
do these new cells arise? Are they derived from odonto- 
blasts, or are they derived from the connective tissue cells 
of the pulp? Dr. Robertson inclines to the belief that they 
arise from the pulp cells. 'If we trace the layer of odonto- 
blasts, we find that as the dentine becomes thinner so the size 
of the dentine-forming cells decreases, till at the lower limit 
of the dentine they are small spindle-shaped cells attached 
to the dentine by their distal processes. Even below the 
extreme limit of the dentine we can still follow the line of 
odontoblasts downwards as a layer of fusiform connective 
tissue cells, gradually become smaller till they fade imper- 
ceptibly into the pulp tissue. There is no line of demarca- 
tion between them and the ordinary small round cells of the 
pulp." 

"The question now is, How are we to explain how the tooth 
has increased so much in size? There appear to be four proc- 
esses all at work at the same time in the growing tooth. These 
processes are: 

(i) Increase in length of the tooth by an addition of new 
dentine at the lower end of the root. This addition 
more than compensates for the loss caused by the 
grinding down of its crown. In adult age, the growth 
of new dentine and the wearing down balance one 
another, and the tooth therefore remains of constant 
length, 
(ii) Increase in width of the tooth by. the gradual widen- 
ing of the "formative ring;" 
(iii) A slight interstitial increase in the dentine, causing 



294 DENTAL HISTOGENESIS 

the formation of an increased amount of matrix be- 
tween the tubules. This interstitial increase appears 
only to occur in the very young tooth. 
(iv) As the tooth grows, new layers of dentine are depos- 
ited on the inner surface of the already existing den- 
tine. This deposit is probably due to the influence 
of odontoblasts, since they are concerned in the pro- 
duction of dentine from the beginning. 
"As the entire tooth is pushed onwards by the growth of 
new dentine at its lower end, the crown is continually being 
worn down in grinding. The upper end of the pulp cavity is 
very narrow and contracted, owing to the large amount of 
dentine which has accumulated on its surface, for in this situ- 
ation the dentine is of oldest date and so is thickest. Un- 
less provision were made to prevent it, the pulp cavity would 
soon become exposed by reason of the grinding down of the 
crown. It is here, however, at the upper part of the pulp 
cavity, that the dentine reaches its maximum thickness, and 
so reduces the diameter of the pulp cavity, that it persists 
only as a fine channel of considerable length leading from 
the pulp cavity to the free surface of the tooth. Osseous 
tissue is developed in this channel, which, together with many 
small round cells and capillaries, prevents any direct com- 
munication between the surface of the tooth and the pulp. 
No odontoblasts remain in this connecting channel; therefore, 
since the dentinal fibres in the crown of dentine have lost 
their connection with nerves the grinding surface of the rabbit's 
incisor has lost sensitivity. These laminae of bone which help 
to block up the remains of the pulp-cavity at the apex of the 
tooth may be part of the layer of cement which, in the persist- 
ently growing teeth of many animals, covers over the crown of 
the tooth, and which may when worn away sink into the almost 
occluded apex of the pulp-cavity and grow there. It may, 
however, be developed directly from the tissue of the pulp. 

"In the adult rabbit's tooth, then, the growth of dentine at 
the 'formative ring,' the continual deposition of new dentine 
on the inner surface of the old, and the extent to which the 
tooth is worn down externally, exactly balance one another, 



development of teeth in Mammalia 



295 



and thus the tooth remains of the same size throughout life. 
In the young growing animal, however, the first two of these 
processes exceeds the third, and so the tooth grows greatly 
in length, diameter, and thickness of dentine. 

"Having seen how a simple conical tooth increases in size, 
the next question which naturally arose was, How do flask- 
shaped teeth, such as the canine tooth of a cat, increase in size? 
To answer that question, the canine tooth of the lower jaw 
was examined in (i) a newly born kitten; (ii) in a kitten of 
one month old; and (iii) in the adult cat. These teeth in 
the cat, as in all Carnivora, are shed at an early period of ex- 
istence. This introduces a slight fallacy, for it compels one 
to compare deciduous with permanent teeth. 



Measurements of Lower Caxixe Teeth in Cats 





Newly born 


One month old 


Adult 


Totallength of tooth. . 
Greatest length of pulp 


% inch 0.196 
%o inch 0.18 
K25 inch 0.056 


18 Hoo inch 0.366 

?25 inch 0.32 

3 J-ioo inch .074 


s Koo inch 0.59 
H inch 0.5 
H5 inch 0.04 


Greatest breadth of 


Thickness of dentine 


at middle of tooth . . . 
Greatest thickness of 


K200 inch 0.006 


?250 inch .036 


'iio inch .06 


dentine at crown. . . . 
Diameter of dentinal 


Ho inch .0166 


z ?'5 inch 0.046 


%oo inch 0.09 


tubules at origin 


J-17000 inch 0.0000589 


H7000 inch 0.0000589 


at base H2000 inch 

0.0000833 
at crown H7000 inch 


Width of intertubular 






.000037 


dentine 


^4250 inch 0.000235 


3-4250 inch 0.000235 


at base J-42 50 inch 

0.000235 
at crown J-6000 inch 

0.000166 



This table shows that (i) The lower canine tooth of the 
adult cat is fully three times as long as it is in the newly 
born kitten. 

(ii) The pulp cavity grows longer in the same propor- 
tion. 

(iii) As regards the width of the pulp cavity, it seems first 
to increase in breadth, but in the adult tooth the breadth 
is less than in the newly born kitten. 



296 DENTAL HISTOGENESIS 

(iv) At the middle of the tooth the dentine increases to a 
thickness ten times greater than in the newly born 
kitten; while at the crown it increases to about six times. 
(v) The diameter of the dentinal tubules was the same 
in the young kittens. In the adult cat, however, 
the tubules at the base of the tooth are one-half larger 
than those of the younger cats; but near the crown 
their diameter decreases greatly, being a half less than 
in the younger cats, and even two-and-a-half times 
smaller than at the base of the same adult tooth. 
(vi) The width of the intertubular substance remains the 
same in the canines of kittens and also at the base of 
the adult tooth. At the crown of the adult tooth, 
however, it is only three-fourths of the breadth of what 
it is at the root, or in the younger teeth. 
"Before describing how this tooth grows, particular atten- 
tion must first be directed to a fact on which the importance of 
this inquiry rests, viz., this, that the canine tooth of young 
kittens is not flask-shaped, but merely conical, resembling 
the extinguisher of a candle, the sides sloping downwards and 
outwards from the crown. This originally conical tooth in- 
creases in size as follows: 

1. By the gradual dilatation of the 'formative ring' of cells 
at the base of the dentine it is increased in diameter. 

2. It is increased in length by the addition of new dentine 
at the base of the tooth and the consequent elevation of the 
whole tooth. This also is due to the action of the formative 
ring. 

"These two processes go on simultaneously, and so the base 
of the tooth is always growing larger while the tooth is grow- 
ing in length. This outward extension of the basal formative 
ring of odontoblasts goes on till a maximum is reached. This 
broadest part of the pulp in the growing tooth of the kitten 
is at the base, while in the adult cat it remains about the middle 
of [the tooth. Thus in the newly born kitten the broadest 
diameter of the pulp cavity was at the base of the conical 
tooth, and measured 0.056 inch. In the kitten one month old, 
the basal diameter of the pulp was still the greatest, the tooth 



development of teeth in Mammalia 297 

still being conical, and measured 0.074 inch. It had not yet 
become flask-shaped, but about this time the pulp cavity attains 
its greatest breadth and afterwards diminishes. The elongation 
of the tooth still continues, but the formative ring now gradually 
contracts, and thus forms an inverted basal cone and so leads 
to the production of the flask. The narrowing of this basal ring 
continues until, in the adult, it becomes a small ring surrounding 
the vessels and nerves going to the pulp. The elongation of 
the tooth has also caused its broadest part to be situated about 
midway between crown and base. Thus the tooth is made up 
of two cones joined at their bases, the 'crown-cone' being 
formed by a dilatation of the 'formative ring' and the 'root-cone' 
by the gradual narrowing of the ring. 

"3. During the whole time that the tooth is growing in 
length, a constant deposition of new dentine is taking place 
on the inner surface of the old. Thus the maximum diameter 
of the pulp cavity in the young tooth becomes lessened, till, 
in the adult, the original pulp cavity is much reduced in size 
compared with its width in the newly born kitten. Having 
reached this stage the processes of growth cease, and thus a 
typical flask-shaped tooth is produced. We see now how the 
apparent anomaly regarding the width of the pulp cavity 
arises. From the table we find that the width of this cavity 
is less in the adult tooth than it is in the new-born kitten. 
This is due to the large deposit of new dentine on the inner 
surface of the old, causing such a narrowing of the pulp cavity 
that the above condition is produced. 

"4. It is also shown that there has been an interstitial 
change. The dentinal tubules are smaller and closer together 
near the crown of the adult tooth than near the base. At the 
base the amount of intertubular dentine remains the same as 
it is in the younger cat's tooth, though the tubules themselves 
are a good deal larger in diameter than in the earlier conditions. 

"Regarding root-formation, we have seen how a single 
rooted tooth, as the canine, is developed by the gradual nar- 
rowing of the basal dentine-forming ring. If, however, this 
formative ring, having reached its maximum dilatation, be- 
comes constricted at two opposite points till these meet like a 



2gS DENTAL HISTOGENESIS 

figure-of-eight; then two smaller formaline rings are produced. 
If these both go on forming dentine and diverging from one 
another, we have two 'root-cones' produced, springing from one 
body and giving us a double rooted tooth. In a similar manner, 
if the formative ring becomes sub-divided into three or four 
rings, we have a three or four rooted tooth resulting. The tooth 
capsules themselves, even of the molar teeth, are quite simple 
and show no indication of roots. It is only after the body of 
the tooth has been completed that the roots are produced. 
"This inquiry shews that the growth of a tooth is only to a 
very slight extent interstitial. Interstitial growth is seen in 
the incisor tooth of the rabbit, where the dentinal tubules 
become further separated by an increase of dentinal matrix, 
but this appears to take place only in the young tooth. Prob- 
ably it causes a slight increase in the size of the rabbit's 
tooth. In the cat, however, it does not cause any increase in 
the size of the tooth; the width of the intertubular substance 
remains the same. It is only in the upper part of the adult 
tooth that the tubules are smaller and more closely packed. 
All we can affirm in this case is that the interstitial increase 
of the matrix simply encroaches on the size of the tubules 
and so does not cause any increase in the size of the tooth. 

EXAMINATION OF THE TEETH OF YOUNG RABBITS 
FED ON MADDER 

While working at this subject Professor Haycraft gave 
Dr. Robertson the teeth of three young rabbits which had 
been fed on madder for a fortnight. He carefully examined 
these, as he thought they might throw some light on the mode 
of growth in teeth. 

I. The first rabbit was killed after being fed on madder 
for two weeks. All the stained part of the tooth is that pro- 
duced while the madder was added to the food. In the section, 
this staining reached the very crown of the tooth, but only at 
the centre. This clearly demonstrates that there is a constant 
deposit of new dentine on the inner surface of the old. At the 
apex of the pulp cavity the colour is deepest, for most of the 



DEVELOPMENT OF TEETH IN Mammalia 2QQ 

new dentine was deposited in that situation. It is also seen 
that there is a narrow band of stained dentine which immediately 
surrounds the pulp. These teeth also shew that the incisor 
teeth increase in length much more rapidly than the others; 
for, while the incisor is stained in three-fourths of its length, 
the premolar is stained in only half its length. 

II. The second rabbit was fed for two weeks on madder, 
and then on ordinary food for a similar period. The lower 
part of the incisor tooth, and also a narrow strip of dentine 
surrounding the pulp cavity and extending up to the grinding 
surface, is now unstained. This is all new dentine, formed 
during the last two weeks of the animal's life. In the pre- 
molar the axial staining is hardly yet worn away. The deeper 
staining of the dentine on the concavity of the incisor may be 
due to the more rapid growth which there is in this situation, 
and the greater consequent absorption of the circulating stain. 

III. The third rabbit was also fed on madder for two weeks, 
then on ordinary food for three weeks. The teeth shew merely 
a further development of what No. II. did. These madder- 
stained teeth corroborate entirely the explanation of the growth 
of the dentine which has been already given. 

The results of this investigation into the growth of teeth may 
be thus summarised. There is: 

i. Increase in the length of the tooth by addition of new 
dentine at its base; 

2. Increase of diameter by dilatation of the basal formative 
ring. In the case of teeth with roots, these are produced by 
the gradual contraction of this ring with or without sub- 
division; 

3. Deposit of new dentine on the inner surface of the old; 

4. A slight increase in the matrix of the dentine by interstitial 
growth. 

THE GROWTH OF THE INCISOR TEETH OF THE ALBINO RAT 

This has been carefully studied by Drs. W. H. F. Addison, 
and J. L. Appleton, Jr., of the University of Pennsylvania, 
Philadelphia, who in an elaborate paper, "The Structure and 



300 DENTAL HISTOGENESIS 

Growth of the Incisor Teeth of the Albino Rat," Journal of 
Morphology, Vol. 26, 1915, have arrived at the following con- 
clusions: 

"The rate of growth of the upper and lower incisor teeth 
of Mus norvegicus albinus, in the mature animal, averages 2.2 
and 2.8 mm. per week, or 12.5 cm. and 14.5 cm. per year, 
respectively. 

"Growth is due primarily to the proliferation and growth 
of cells at the basal end of the enamel-organ, where new enamel- 
forming cells arise, and at the basal end of the dental papilla 
where new dentine-forming cells develop. 

"The enamel-organ of the adult forms a narrow circular band 
around the basal end of the tooth, and extends forward from 
this on the labial side only. It coincides in its lateral bound- 
aries with the enamel, and extends along the entire imbedded 
portion of the tooth. Anteriorly, it comes in contact with the 
epithelium of the gingival margin, and is carried out continually 
as a narrow band of cells lying on the enamel, between the 
latter and the gingival epithelial tissue. 

"The first indication of the tooth band of the incisors appears 
in 14-day-old foetuses. In foetuses 21 days of age (just before 
birth), enamel and dentine formation is beginning. In animals 

I day old the upper and lower teeth measure 2.3 and 3 mm. 
At 8 to 10 days the teeth erupt, and at 10 days measure 7 and 

II mm. respectively. This period is therefore characterised by 
the rapid elongation of the teeth. 

"The process of attrition begins within a few days after erup- 
tion, so that by 19 or 21 days of age, the typical occlusal surface 
is formed. Up to the time of eruption the anterior end or apex 
of the tooth is immediately under the oral epithelium, while 
the basal or growing end is continually progressing posteriorly. 
After eruption, the basal end becomes nearly stationary in 
position, while the whole tooth structure is continually moving 
forward. The extra-gingival length of the tooth is kept con- 
stant, however, by the attrition of the occlusal surface, either 
through use in gnawing or by the action of the opposing teeth. 

"The histogenesis of the enamel-organ is practically com- 
pleted by the fourth day after birth, although it does not attain 



development of teeth in Mammalia 301 

its final relations to the tooth as a whole, until after eruption. 
In the 18-day foetus the enamel-organ is similar in all parts, 
and the cells of the inner layer measure the same, both lingually 
and labially. From this period forwards, however, the labial 
portion continues to progress towards its fully differentiated 
functional structure, while the lingual portion retrogresses, un- 
til at 4 days after birth the latter is disrupted, by the ingrowth 
of the surrounding connective tissue. Contrasting the cells of 
the inner layer — the potential ameloblasts — on the labial and 
lingual sides, they are practically the same in the 18-day foetus, 
but at 19 days they are found to measure 24 and 20 n respec- 
tively. In the 21-day foetus, they measure 30 to 34 and 12 n, 
and 1 day after birth the true ameloblasts on the labial side 
have increased to 40 p., while the non-functional cells of the 
lingual side are only 10 n in height. At 4 days, the latter cease 
to form a continuous layer, by reason of the dispersion of the 
cells by the surrounding connective tissue, except at the basal 
formative region. 

"Characteristic of the permanently-growing enamel-organ 
are the epithelial papillae, formed by the elevations of the outer 
layer of the enamel-organ, and the cells of the enamel pulp. 
Between these elevations are numerous capillaries which insure 
a rich blood supply to the enamel-forming cells. 

"There are three layers in the functional enamel-organ — 
inner, middle and outer. The inner is constituted of the tall 
ameloblasts, and the middle is made up of two divisions, (a) 
stratum intermedium and (b) enamel pulp. The latter unites 
with the single layer of cuboidal cells which compose the outer 
layer, to form the epithelial papillae. 

"The apex of the primitive tooth is formed of a variety of 
secondary dentine — 'osteo-dentine' of Tomes — which is softer 
than true dentine, and differs in its structural arrangement. 
After eruption, this terminal portion of osteo-dentine is soon 
worn away by attrition, and the typical occlusal surface is 
developed, as seen at 19 or 21 days. At 21 and 23 days the 
first two molars erupt in both upper and lower jaws, and from 
now on, the animal is able to secure food for itself, and if 
necessary can maintain an independent existence. 



302 DENTAL HISTOGENESIS 

"As the tooth continues to be worn away there is a provision 
for the continual filling in of the apex of the pulp-chamber by 
the formation of what may also be called osteo-dentine. This 
is a form of secondary dentine, containing, when first formed, 
cells and blood-vessels. This is always at a little distance, 
about i mm., from the occlusal surface, but as any part of the 
tooth, in its outward progression approaches the occlusal sur- 
face, the soft elements disappear within the osteo-dentine, and 
the latter forms a hard continuous surface with the adjoining 
true dentine. The position of this osteo-dentine is marked as 
a line on the occlusal surface of the teeth. 

"Prior to eruption there develops around the apex of the 
tooth, as it lies in contact with the surface epithelium, a thick- 
ened ring of stratified epithelium. This ring of tissue is pierced 
by the apex (i.e., cutting or incisive edge) of the tooth at erup- 
tion, and would seem to have the function of serving as a 
resistant margin for the soft tissues, and of preventing other 
tissues being carried along with the erupting tooth. 

"The length of the teeth varies with the size of the cranium, 
so that the persistent growth is not only sufficient to offset the 
continual attrition, but also serves to keep the length of the 
teeth in a definite relation to the length of the skull, as the 
latter increases in size. 

"The lower tooth is always longer than the upper, and this 
difference manifests itself even in the tooth-bands of these 
structures in the 19-day foetus. 

DEVELOPMENT OF THE CEMENTUM 

Of this there need be but little said; mere repetition of 
descriptions of phenomena which are probably now under- 
stood with the greatest certainty, is needless. Suffice it to 
say, that there is every reason to believe that cementum is 
developed ordinarily after the manner of intramembranous 
ossification of bone. Where thick layers of the tissue exist 
over the crowns of teeth, Magitot's opinion that develop- 
ment and ossification in a cement organ of fibro-cartilaginous 
character is most probably accurate. 



development op teeth in Mammalia 



303 



THE STAGES OP DEVELOPMENT OF THE JAWS AND TEETH IN A 
HUMAN EMBRYO OF HALP-TERM 

For the purpose of investigation, and in order to put on 
record a careful account of the degrees of development arrived 
at, at a certain period of growth, the right half of the upper 
jaw of a human fcetus of about 20 to 25 weeks was employed. 



SB 


] 
* g|U| 1 

r . ' 111 

!l \ ' 1 

, ■ • 1 ; ) P 

1 

' ,f i j 
11 Ifi f ji 





Fig. 249. — To show an early stage in calcification of cementum. Magnified 
500 times. A. Granular layer of Tomes partly calcified; b. Young cementum. 
(Photomicrograph by Norman Broomell.) 



This was apparently absolutely normal, and, as far as could 
be ascertained, believed to be unaffected by rachitis, syphilis, etc. 
The jaw was subdivided into seven sections, beginning at 
the front, in a sagittal, and behind, in a coronal direction, and 
included the following regions, enclosing deciduous teeth: — 1, 
first incisor; 2, second incisor; 3, canine;. 4, anterior molar; 
5 and 6, posterior molar, and 7, behind the posterior molar, 
near the maxillary tuberosity. The latter showed no dental 



3°4 



DENTAL HISTOGENESIS 




Fig. 250. — From region of first maxillary deciduous incisor. Magnified 
30 times. For description of this and following figures, see Tables A. and B. 
on pp. 306 and 307. 



development of teeth in Mammalia 



305 



structures whatsoever. The figures at the heads of the fol- 
lowing columns indicate these various regions (see pp. 306 and 

3°7)- 

Carefully decalcified and embedded in paraffin, the tissue 
was cut serially, and typical mesial vertical sections selected 




Fig. 251. — From region of second incisor as in preceding figure. Magnified 
30 times. P.z. Permanent tooth germ; e.p. Epithelial "Pearl" or " Gland of 
Serres." 



for pictorially and verbally illustrating the phases of devel- 
opment. It will be observed that in consequence of the action 
of reagents some shrinkage of the embryonic dentine germ has 
taken place. To prevent tautology, brief tables only need here 
be introduced. 



THE HISTOGENESIS OF OVARIAN TEETH 

Not much is known as to the development of those anoma- 
lous misshapen dental structures found in the oophoronic cysts 
of the human ovary. Sir John Bland-Sutton has, however, ex- 



306 



DENTAL HISTOGENESIS 



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development of teeth in Mammalia 



3°7 



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Depth of apex of 
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from free oral 
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3 o8 



DENTAL HISTOGENESIS 




Fig. 252.— From region of canine, as in preceding figure. Magnified 30 times. 



development of teeth in Mammalia 



3°9 




Fig. 253. — From region of deciduous first molar, as in preceding figure. 
Magnified 15 times, e.p. Epithelial "Pearl" or "Gland of Serres." 




Fig. 254. — From region of deciduous second molar, as in preceding figure. 
Magnified 15 times. 



3io 



DENTAL HISTOGENESIS 




Fig. 255. — From posterior portion of region of deciduous second molar as in 
preceding figure. Magnified 10 times. 



development of teeth ix Mammalia 



311 



amined many specimens. These are fully described in his 
"Tumours, Innocent and Malignant," 1906. The accom- 
panying Fig. 256, taken by permission from his work, shows 




Fig. 256. — Composite drawing of the microscopical appearances in a teratomat- 
ous cyst of the ovary, e.o. Enamel organ; d.p. Dentine papilla; e. p. Epithelial 
pearl. 



the component parts in the formation of a tooth. Cf. the 
"Epithelial Pearl" (e.p.), with the same bodies in Figs. 251 
and 253. These are regarded by Bland-Sutton as enamel 
organs. 



CHAPTER XIII 

DEVELOPMENT OF THE TEETH IN PISCES, REPTILIA 
AND BATRACHIA 

Microscopical Elements in: Developing Teeth of (i) Cod; (ii) Dog- 
fish; (iii) Crocodile; (iv) Lizard; (v) Snake; and (vi) Newt. 



In Pisces 

Fishes are vertebrate animals which live in water, and breathe the air 
dissolved in the water by means of gills or branchiae. The two-chambered 
heart consists of a ventricle and auricle or atrium. The limbs, excepting 
in the Cyclostomata and Leptocardii (which are apodal), are modified into 
fins, supplemented by unpaired median fins. The skin is either naked, 
scaly, or covered with osseous plates. Fishes, as a rule, are oviparous. 
The class of Fishes is divided into the following: 1 — 
Sub-class I. Elasmobranchii. 
Order i. Proselachii. 
Order 2. Acanthodides. 
Order 3. Selachii. 

Sub-order 1. Notidani. 
Sub-order 2. Squali. 
Sub-order 3. Raii. 
Order 4. Pleuracanthodes ( = Ichthyotomi). 
Sub-class II. Holocephali. 
Sub-class III. Ostracodermi. 
Order 1. Heterostraci. 
Order 2. Osteostraci. 

Order 3. Pterichthyomorphi ( = Antiarcha). 
Sub-class IV. Dipnoi. 

Order 1. Ctenodipterini. 

Order 2. Monopneumones. 

Order 3. Dipneumones. 

Order 4. Coccosteomorphi ( = Arthrodira). 

1 This is the classification adopted (1908) by Sir E. Ray Lankester and Dr. 
Ridewood of the British Museum (Natural History Department). 
312 



DEVELOPMENT OF TEETH IN Pisces 313 

Sub-class V. Teleostomi. 

Order 1. Stylopterygii* ( = Crossopterygii, auct.). 
Sub-order 1. Tarrasioides ( = Haplistia). 
Sub-order 2. Holoptychioides (= Rhipidistia). 
Sub-order 3. Ccelacanthoides ( = Actinistia). 
Sub-order 4. Polypteroides ( = Cladistia). 
Order 2. Astylopterygii.* 

Sub-order 1. Sturioniformes ( = Chondrostei). 
Sub-order 2. Amiiformes ( = Protospondyli). 
Sub-order 3. Lepidosteiformes ( = ./£theospondyli). 
Order 3. Neichthyes ( = Teleostei). 
Grade A. Physostomi. 
Sub-order 1. Salmoni-clupeiformes ( = Isospondyli). 
Sub-order 2. Cyprini-siluriformes ( = Ostariophysi). 
Sub-order 3. Symbranchiformes. 
Sub-order 4. Anguilliformes ( = Apodes). 
Sub-order 5. Esociformes ( = Haplomi). 
Grade B. Physoclisti. 

Sub-order 6. Halosauriformes ( = Heteromi). 
Sub-order 7. — Gastrosteiformes ( = Catosteomi). 

Division 1. Selenichthyes. 

Division 2. Hemibranchii. 

Division 3. Lophobranchii. 

Division 4. Hypostomides. 
Sub-order 8. Mugiliformes ( = Percesoces). 
Sub-order 9. Gadiformes ( = Anacanthini, in part). 
Sub-order 10. Acanthopterygii. 

Division 1. Perciformes. 

Division 2. Scombriformes. 

Division 3. Zeorhombiformes. 

Division 4. Kurtiformes. 

Division 5. Gobiiformes. 

Division 6. Echeneiformes ( = Discocephali). 

Division 7. Trigliformes ( = Scleroparei). 

Division 8. Blenniiformes ( = Jugulares). 

Division 9. Trachypteriformes ( = Tseniosomi). 

Division 10. Mastacembeliformes ( = Opisthomi). 
Sub-order n. Lophiiformes ( = Pediculati). 
Sub-order 12. Balistiformes ( = Plectognathi). 

It is unnecessary, in a work of this character, to give more 
than a brief outline of the manner in which the teeth of Fishes 
are^evolved. The simplicity of the process is remarkable 

* These are often spoken of as "Ganoid Fishes." 



314 DENTAL HISTOGENESIS 

and of interest, especially when the development and succession 
of teeth in Mammalia have been studied. 

Two examples need only be here detailed. 

One occurs in the Teleostomi, the other in the Elasmobranchii. 

In Teleostomi 

Example. — Order — Neichthyes. Sub-order — Gadiformes, in 
the division Gadidae (Cod-fishes). 

The simplest arrangements of parts are well exhibited in 
the jaws of young Cod-fishes of about 10 cm. body length. 
Gadus luscus may be taken as a type. 

Under low powers the oral epithelium is very remarkable 
for its depth and strength; its thickness may exceed that of 
the sub-mucous tissue. The free surface is somewhat thrown 
into wrinkles or folds. The deeper layer of cells is of the 
usual columnar shape. The submucous tissue extends into the 
former in the shape of many narrow numerous papillae. 

The tooth germs, originating de novo, are developed in the 
tissue which fills a papilla, which, with the growth of the germ, 
becomes widened and flattened. 

Minute Structure of Tooth Germ. — There is no tooth band and 
no heaping up of epithelium. An ill-constituted enamel organ 
exists, the stellate reticulum of which is of a rudimentary char- 
acter, consisting merely of strands of fibres; no cells and no 
nuclei fill the inter-spaces. The ameloblasts are short cylinders 
with large oval nuclei separated from a well-defined stratum 
intermedium by a clear narrow zone. 

The odontoblasts are prominent. At the base of the den- 
tine germ, the mesodermic cells about to form the pulp are 
sharply differentiated from the underlying structures, and no 
dental capsule, as such, occurs. The odontoblasts of mature 
teeth are rounded or flattened, adhering closely to the dentine, 
and in a striking way resembling osteoblasts. They are not 
distinguishable from the pulp cells in any other particular than 
their position. These same cells in younger teeth shew tran- 
sitional changes from these round forms to long cylindrical 
cells, whose nuclei are not particularly marked. 



DEVELOPMENT OF TEETH IN Pisces 



315 



In the Gadidcz (e.g., Gadus Morrhua) Rose 1 describes the 
odontoblasts as extraordinarily long and thin cells in the 
young tooth rudiments. But Fig. 3, which accompanies his 
paper, shews the cells to be longest and thinnest over the 
deepest base of the dentine, and gradually diminishing in 
length and width as they approach the cutting edge. 

In every section of Gadus luscus prepared by the author 
this is not the case. The cells half-way down the young tooth 



Y T 




Fig. 257. — Vertical section through jaw of a young cod fish. Prepared by- 
hardening and decalcification. Stained with Ehrlich's acid ha.'matoxylene. 
Magnified 50 times, o.t. Oldest tooth germ; o. Odontoblasts, in several layers, 
at base of tooth; y.t. Youngest tooth germ; o.e. Oral epithelium; b. Bone of the 
jaw. 



germs are the largest, those at the oral edge and at the base 
smaller and rounder, till at the extreme limit of the develop- 
ing pulp, they are flat and scale-like and adherent to the den- 
tine. Inspection of the photomicrograph, however, at first 
sight would seem to indicate that Rose's description is correct. 

1 "On the Various Alterations of the Hard Tissues in the Lower Vertebrate 
Animals." Translated from the Anatomischer Anzciger, in the Journal Brit. 
Dent. Assoc, Jan., 1899. 



316 DENTAL HISTOGENESIS 

But the appearances here produced are due to several layers 
of small cells, which become curiously congregated in this 
way. The chief point is that the nuclei are in no sense of the 
word increased or elongated. 

In structure the dentine is vitro-dentine, according to Rose. 
(For the meaning of this term see p. 108). In the cases just 
noted it (the dentine) possesses no canals, scanty tubes, but 
faint laminations. The tooth germs move in an outward 
direction, and when fully completed are found perched on the 
pedestal of bone known as the "bone of attachment." 



In Elasmobranchii 

Example. — Order — SelacJiii; sub-order — Squali; family — 
Scylliidce (Dogfish). 

Specimens of Scyllium caniculum afford excellent types of 
the genesis, evolution and eruption of the teeth. 

The epithelium of the mouth is not flat, as in Mammalia, 
but is beset with myriads of elevations of microscopic size. 

The outermost layers are not particularly cornified. 

At varying distances there occur on the outer surface of the 
lip, the dermal spines, each of which is imbedded by means of a 
widened broad base in the submucous tissue. In some places 
their close association causes these spines to become imbricated. 

The accompanying photomicrograph shews the remarkable 
analogy between the teeth and these placoid scales or dermal 
denticles. In fact, the latter may all be considered modified 
teeth, differing chiefly in function and positions (see Fig. 258). 

In addition to the variation in their positions, these spines 
are modified in regard to shape, size, and structure. 

In form, the greater number which cover the surface of the 
skin of the animal are flattened plates, with a slightly convex 
free margin, and wedge-shaped bases securely dovetailed 
into the firm dermal connective tissue. 

On the edge of the jaw the exposed portion becomes rounded 
and presents a fungiform outline, while at the place of inflexion 
over the jaw margin it assumes the appearance of the flattened 



DEVELOPMENT OF TEETH IN Pisces 



317 




Fig. 258. — Vertical section through the jaw of a young dogfish. Prepared 
by hardening and decalcification. Stained with borax-carmine and Ehrlich's 
acid hEematoxylene. The vertical lines are markings made by a dull razor 
during cutting on an ether-freezing microtome. Magnified 25 times, c. Carti- 
lage of the jaw, with semi-ossified external crust; d.e. Epithelium of the skin; 
o.E. Epithelium of the mouth; l.z. Lowest extent of the tooth band; d.p. Dentine 
papilla of young tooth germ; f.t. Functional tooth; s. Two teeth about to be shed; 
p.s. Pulp tissue in centre of a dermal denticle, a. Aperture at base of dermal 
denticle for passage of blood-vessels to the pulp. 



318 DENTAL HISTOGENESIS 

head and beak of a bird. In size, the latter are by far the 
larger. 

In structure, each denticle, similarly to each dental organ, 
possesses a central pulp chamber, filled with abundant round 
cells and a fairly well organised blood system. The hard 
parts contain dentinal tubes, which radiate in the usual way. 

The epithelium of the mouth is considerably deeper than 
that of the skin, and extends almost to the base of each tooth; 
for here, at the oral border, the denticles become teeth in func- 
tion, being merely transitional in structure. It embraces the 
teeth very intimately. An aperture at the side of the base 
admits the passage of blood-vessels to the pulp. 

The tooth band is continuously growing, and dips down 
deeply as far as the curved recess of the cartilaginous frame- 
work of the jaw. Here, as in the deepest locality, are the 
youngest teeth germs. This tooth band is of great thickness, 
and is highly specialised. It extends as a broad column down 
the side of the jaw cartilage, and in it are the developing teeth. 

In the dogfish the deepest layer of the tooth band produces 
the ameloblasts as in other creatures; and the next deepest layer 
of cells forms what must be analogous with the stratum inter- 
medium of mammalian enamel organs. 

Throughout, the deepest layer is composed of long cylin- 
drical cells closely packed together, containing oval or flattened 
granular nuclei. The external layer is very short and the nuclei 
are correspondingly abbreviated. 

By counter-staining, the young teeth may reveal what is 
probably a thin superficial band of enamel. 

The dentine and the pulps of the teeth are developed from 
the connective tissue. The cells in the situation of the future 
dentine papilla become approximated, and in the pulps, while 
still retaining their rounded forms, can be easily seen to deposit 
ossific material on the sides of the connective tissue scaffolding 
of the dentine. 

In the interspaces of the developing teeth, the deepest layer 
is arranged like a loop. 

Thus, enamel organs as highly specialised as in Mammalia, 
are non-existent and no dental capsules surround the papilla?. 



DEVELOPMENT OF TEETH IN Reptilid 319 

II 

In Reptilia 

The class of Reptiles is divided into the following orders: — i., Crocodilia; 
ii., Rhynchocephalia; Hi., Lacertilia; iv., Ophidia; and v., Chelonia. 
In i. (Crocodile, Garial, Alligator) the teeth are implanted in sockets; 
in ii. (New Zealand Lizard or Sphcnodon punctatus) they are anky- 
losed to the summits of the jaws, the bone at their bases undergoing a 
secondary upgrowth (hyperacrodont), 1 but are soon lost by attrition, 
their functions being carried on by the dense free margins of the 
maxilla and mandible; in iii. (Lizards) they are ankylosed and non- 
socketed; and in iv. (Snakes) the same; while in v. (Turtles and 
Tortoises) they are absent . 

In Crocodilia 

The genesis of the teeth in Crocodiles resembles in a marked 
degree that of mammalian animals. An exhaustive descrip- 
tion would be, in the main, little better than a mere recapitula- 
tion of the story. Suffice it to say that the teeth succeed ver- 
tically, being thecodont — i.e., contained in the same socket. 
Absorption of the functional tooth by its successor takes place, 
owing, no doubt, to some form of absorbent organ, as in man. 
It is interesting to compare photomicrographs of these two 
conditions. (See Figs. 233 and 259). 

In Lacertilia 

The common English Green Lizard (L. viridis) may be 
employed as a type. 

The chief characteristics are the great length of the tooth 
band, and the consequent depth of the enamel organ and dentine 
germ. As far as the maxilla is concerned, the whole tooth 
germ is placed as closely as possible to a concavity in the upper 
and inner surface of the jaw at the base of the functional tooth. 

The ameloblasts are considerably elongated, and extend 
deeply down the sides of the dentine germ. The layer is 
continuous, as in man, with the external epithelium. There 

1 See paper by Howe and Swinnerton on "The Development of the Skeleton 
of the Tuatera." Trans. Zoological Soc, Feb., 1901. 



3 2 ° 



DENTAL HISTOGENESIS 




Fig. 259. — Vertical section of mandible of young crocodile. Prepared by 
hardening and decalcification. Stained with borax-carmine and Ehrlich's acid 
haematoxylene. Magnified 20 times, d.f. Dentine of functional tooth; d.s. 
Dentine of successional tooth; b. Bone of jaw; m. Mucous gland. 



DEVELOPMENT OF TEETH IN Reptilici 



3 2I 



is no stellate reticulum in the otherwise well-differentiated 
enamel organ, but the intermediate space is occupied by a 
few cells with elongated nuclei. Apparently no cells analo- 
gous to the stratum intermedium exist. 

The continuation of the tooth band is in a line with the 
deep part of the external epithelium of the enamel organ of 




DPS 



Fig. 260.— Vertical section of jaw of an acrodont lizard. Prepared as in 
preceding figure. Magnified 25 times, d.f. Dentine of functional tooth; d.p.S. 
Dentine papilla of successional tooth germ; o.e. Oral epithelium; c.z. Continu- 
ously growing tooth band; b. Bone of jaw to which the functional tooth is 
ankylosed; M. Mucous gland. 



the neighbouring young tooth germs, and in direct conti- 
nuity with the deepest layer of cells of the original tooth 
band. 

The dentine germ is made up of a dense mass of oval cells, 
which at the periphery are somewhat elongated. 

The submucous tissue by condensation of its cells and 
fibrous tissue produces an "adventitious capsule." 



322 



DENTAL HISTOGENESIS 



In Ophidia 

The bone of the jaw of the common or Ringed Snake (Tro- 
pidonotus natrix) is somewhat pyriform, with a broad flat- 
tened base. The functional tooth surmounts this. Occu- 
pying a site internal to the bone, the young tooth germs are 
found very closely placed, not only to one another, but to 
the body of the bone itself. 




Fig. 261. — Vertical section of jaw of snake. Prepared as in preceding figure. 
Stained with Ehrlich's acid haematoxylene. di. Dentine of oldest tooth germ; 
o. Odontoblasts of the dentine papilla of the same; D2. Dentine of next oldest 
tooth germ; D3. D4. D5. Dentine of younger tooth germs; D6- Dentine of youngest 
tooth germ; b. Bone of jaw; o.e. Oral epithelium; m. Muscle fibres. 



Typical sections shew the oldest tooth germs to be triangular 
in outline, while the developing teeth in vertical sections 
have, as a rule, a circular shape. The oldest of the develop- 
ing teeth in some sections presents a V-shaped outline. This 
apparent morphological difference is due to the fact that the 
circular teeth are cut transversely, and the others obliquely, 
lying as they do in a recumbent or semi-recumbent position 
before they assume the erect attitude. 



DEVELOPMENT OF TEETH IN Batracllid 323 

The great part of the tooth is composed of ortho-dentine. 
The layer of odontoblasts is of interest, inasmuch as the cells 
near the base are the most elongated of all, those at the incisive 
margin being small and round. The tooth band is very short, 
surrounding each germ. It is of continuous growth. 

The oral epithelium differs in a curious fashion from that of 
other reptiles. Here it consists of long, narrow cells, which 
have almost the appearance of ciliated columnar cells. There 
is only one layer, and it is arranged on a sort of basement 
membrane, which is puckered up into folds after the fashion 
of the fungiform papilla? of the tongue. 

Ill 

In Batrachia (Frogs and Newts) 

These animals are cold-blooded vertebrates, which for some, or the whole, 
period of their existence breathe by gills, and in adult life from lungs. 
The heart is tri-lobed, having two ventricle and one auricle. Some are 
ecaudate and apodal. The larva is fish-like and breathes by means of 
gills, which later on are replaced by lungs. Some, however, retain 
their gills, while certain frogs leave the egg in a perfect form. They 
may be oviparous and ovoviviparous. 

They are divided into the following orders: 

(i) Ecaudata — Frogs and Toads, the former of which is edentulous as 

far as the lower jaw is concerned, the latter, as to both jaws, 
(ii) Candata — Newts, Salamanders, &c. 
(iii) Apoda, or Ccecilians. 

The plate and mandibular bones of the newt (Molge vul- 
garis) are extremely thin and delicate. In the median line, 
at its innermost margin, the palate bones are thickest, the 
intervening portions being of remarkable tenuity. 

Development of the teeth begins in the oral epithelium 
which is near the free margins of the bone, by a down-growth 
of epithelium. The tooth band is shallow, but very flat, 
and grows continuously towards the middle line. 

The oral epithelium possesses several characteristics. 

The cells are exceedingly brilliant, being almost transparent 
in nature, that is, the cytoplasm is scarcely granular. This 



3 2 4 



DEXTAL HISTOGENESIS 



makes the large oval nuclei particularly prominent, and helps, 
too, to reveal the karyoplasm and chromatin they contain. 
The phenomena of mitosis may be well studied here. The 
epithelial layer is almost twelve cells deep. There is no cel- 
lular differentiation into a rete Malphigii. 

The constituents of the tooth band are flattened bodies with 
flat nuclei, and they lie more or less in a direction which is 
parallel to the palate. 




Fig. 262. — Coronal section of the head of a newt, with the mandible detached 
and removed. Prepared similarly to the preceding figure. Magnified 15 times. 
O.E. Oral epithelium; f.t. Functional tooth; e.o. Enamel organ of young tooth 
germ, the tooth band being continued beyond it towards the centre of the 
palate; n.f. Nasal fossa. 

In a typical tooth germ which is beginning to assume a defi- 
nite shape, the dentine organ is occupied by an assemblage 
of large elongated cells with reticular nuclei. The dentine 
is formed at a very early period of growth. 

Outside this hard tissue is a layer of smaller rounder cells, 
and outside this is a second layer, separated from the former 
by a clear translucent line or space. 



DEVELOPMENT OF ATYPAL DENTINES 325 

There is hardly any attempt at the formation of an enamel 
organ; if it exists at all, it is an exceedingly rudimentary 
structure. 

In the anterior part of the mouth, the two inwardly ex- 
tending tooth bands of the palate meet and become fused, and 
form a continuous uninterrupted sheet of epithelium, cut off on 
the outer side from the oral epithelium, by a thin band of 
submucous tissue, whose characteristics are small narrow 
cells imbedded in a clear matrix scantily supplied with fibres, 
and forming a succession of young teeth placed side by side 
on the thin jaw bone. The youngest tooth germs are in the 
centre of this band, the oldest at its margin. 

DEVELOPMENT OF VASO- AND PLICI-DENTINE 

The process of development is essentially the same as that 
described in connection with hard or orthodentine (q.v. p. 287). 

It is, however, somewhat modified by the fact that the 
odontoblasts are of rounded shape like osteoblasts (Tomes), 
which deposit calcific material along the bundles of connec- 
tive tissue fibres, which in the case of fishes are most pro- 
nounced on the surface of the pulp. The capillaries remain in 
situ, and the dentine is deposited around them, leaving channels 
in the dentine. 

With regard to plici-dentine, the mode of formation is iden- 
tical, but the capillaries are not conserved in the dentine. 

In Carcharias, as Tomes has pointed out, the organic matrix 
of the outer layer (probably enamel) is furnished by a special- 
ized layer of the dentine papilla, and over this are ameloblasts 
of enormous length. They may measure 70/i or 8om. 

DEVELOPMENT OF OSTEO-DENTINE 

The surface of the pulp is first ossified in the usual way, by 
deposition of lime salts around its odontogenic fibres. Thus 
the outer sheath of hard dentine is manufactured. 

The bulk of the tissue is, however, developed after the 
manner of intra-membranous ossification of bone; that is, 



326 DENTAL HISTOGENESIS 

rods of osseous material run through the long axis of the pulp, 
being continuous externally with the rest of the great fas- 
ciculi of connective tissue fibres which freely traverse the 
central soft organ. As Tomes says {op. cit. p. 202): "Osteo- 
blasts clothe, like an epithelium, the trabecular and the con- 
nective tissue fibres attached to them, and by the calcification 
of these the osteo-dentine is formed." 



APPENDIX 
NOTE A 

ON THE FUNCTIONS OF THE CELLS OF THE PULP 



The questions relative to the functions and uses of the 
odontoblasts are deep and intricate, and for years have been 
the subject of earnest inquiry. Many theories as to their 
properties have been brought forward. 

It will be helpful, for a clear comprehension of what is to 
follow, to briefly enumerate these various opinions. Tomes, 1 
and with him the majority of observers, once believed in (A) the 
conversion theory of the formation of dentine. The cells 
undergo changes and become converted into matrix, sheath 
and fibril. In recent years, however, Tomes has spoken on 
this point with no slight degree of uncertainty. In 1893, he 
remarked, 2 "We have always been accustomed to say that 
they (the odontoblasts) formed the whole of the dentine; now 
we know that they do not." 

Further, Walkhoff 3 expresses his opinion that the dentine 
processes serve essentially for the nutrition of the dentine, 
the forms of the odontoblasts being in complete accord with 
their functional requirements. ("Ihre Formen passen sich den 
jeweiligen Funktionsbediirfnissen durchaus an.") 

Again, many histologists including Magitot, Kolliker, etc., 
hold to (B) the secretion theory, maintaining that the dentinal 
matrix is secreted from these cells. 

1 "Dental Anatomy," p. 170, 1889. 

2 Jour, of Brit. Dent. Assoc, vol. xiv., p. 474. 

' "Die Normale Histologic Menschlicher Zahne," p. 128, 1901. 
327 



328 APPENDIX 

Klein 1 subscribed to the belief that the odontoblasts form 
matrix only, while the fibrils are not their processes, but stretch 
out from a deeper layer of cells. In addition, there is the 
theory of Heitzmann and Bodecker, apparently corroborated 
by Abbot of New York. 2 Here the odontoblasts are said 
to be first broken up into "medullary corpuscles" at their 
distal end, which become infiltrated first with a glue-yielding 
basis substance, and afterwards with lime-salts. Thus many 
conflicting views exist. 

The axiom that dentinal fibrils are considered to be sensa- 
tion conductors is well known to all. Inasmuch, then, as 
they are regarded functionally in the light of nerves, and as 
they represent the peripheral poles of the odontoblasts, and 
are, in fact, part and parcel of those cells, it follows that the 
latter must be concerned in the act of conveying extrinsic 
stimuli to the nerves of the pulp. An odontoblast is more of 
a sensation transmitter than a sensation generator. In other 
words, it is believed to be a means of communication between 
fibril and nerve telodendria — not originating, but passing on sen- 
sory impulses from without in, and warning the pulp, so to 
speak, of incoming dangers. This seems to the author a 
sensible argument, and this is his theory. 

In order to prove this, it is necessary to show (1) that odon- 
toblasts do not form dentine, as is generally understood; 
(2) to prove that they are the end organs of the nerve filaments 
of the pulp. 

Negative Evidences 

The arguments to disprove the dentine-forming theory are 
many and important. They are as follow: 

1. No observer has ever seen a semi-calcified odontoblast, 
or recorded the observation of one secreting a calcareous ma- 
terial, although this has been done over and over again with 
regard to the ameloblasts of the enamel organ, as Tomes 3 
and Leon Williams have demonstrated. 

1 "Atlas of Histology," p. 185, 1880. 

2 Dental Cosmos, Sept., p. 821, 1893. 

3 Op. cit. 



APPENDLX 329 

2. The same cell cannot take on two totally different func- 
tions simultaneously. In general normal histology it is 
found that complex, branched, ganglionic bodies exist in the 
nervous system, while very simple cells — osteoblasts — pro- 
duce the matrix of bone. There must be a separate cell for the 
formation of fibril and matrix. 

3. The presence of spaces between odontoblasts would lead 
one to expect to find like spaces in dentine, but this is not so. 
Per contra, active osteoblasts are closely packed together. 

4. As fibrils and their sheaths are known to cross inter- 
globular spaces, and as the latter are considered to be an arrest 
of dentinal development, one would expect that if the fibrils 
were formed by the same agents as those which produced 
matrix, they themselves (fibrils) would be absent; but this is 
not so. 

5. Again, in the matrix of the dento-genetic zone observed 
on the margins of incompletely developed pulps, fibrils are seen 
most clearly to stretch across the intervening boundary, and 
there is a distinct mark of demarcation between them and the 
homogeneous substance through which they extend. 

6. The granularity of the cells, as has been already stated, 
is visibly unaffected by dilute acids or chemical reagents; 
thus it would seem that calcium salts enter but little into their 
composition. 

7. After decalcification in formic acid, the matrix may be 
torn into laminae, which run parallel to the surface of the pulp 
cavity, whereas they would run at right angles to that surface 
if odontoblasts formed matrix. 

8. The dissimilarity in the shapes and sizes of the cells is 
against the acceptance of this view; this dissimilarity would 
be inexplicable if they formed dentine. Osteoblasts do not 
differ thus. 

9. The fact that nodules of calcific material in the pulp are 
formed by small round cells, and that odontoblasts take no 
part in this work, is clearly seen when sections of pulps con- 
also taining calcareous degenerations are cut in situ. This rule 
obtains in the growth of composite odontomes (see Vol. II). 

10. It is a law that after a cell has ceased its functions, it 



330 APPENDIX 

atrophies and disappears. Here, however, odontoblasts per- 
sist long after all dentine matrix has been completed. 

ii. In some sections of the root, with the pulp in situ, here 
and there odontoblasts are absent. It is remarkable that in 
these situations their corresponding tubules are wanting. 

12. And finally there must be added Underwood's 1 state- 
ments — "that the distinction between fibril and matrix is 
not merely one of a degree of calcification," because it (the 
fibril) is equally observable when the tissue has been formed 
but not calcified; it remains after decalcification; it is present 
in the interglobular spaces where no calcification has occurred; 
"that all traces of the boundaries of the cells are absolutely 
obliterated even in imperfectly developed tissue;" and "that 
the cells and their processes are sharply marked off from the 
surrounding tissues during all the stages of development." 

Positive Evidences 

In order to deal satisfactorily with the evidences which are 
at hand, to show what are the functions of the odontoblasts, 
it is important to take three things into consideration, viz., 
the development of these cells, their relation to the nutrition 
of dentine, and the question whether or not the ultimate ter- 
minations of the nerves have any direct or indirect connection 
with the odontoblasts. 

And here arise the most serious difficulties that surround 
the subject. The odontoblasts, as far as is known, are derived 
from the stomodasal mesoderm, i.e., they are formed on the edge 
of the up-growing papilla of the dentine organ. If it could be 
proved that they arise from ectoderm, one great difficulty would 
be removed, for it would be then quite easy to affirm that they 
are nerve endings or end bulbs, and their analogy to the cells 
at the terminations of the optic and auditory nerves would be 
more striking, not only with regard to their morphology but also 
their physiology. Most authorities agree that the nervous 
system is produced primarily by the ectodermic layer of the 
blastoderm. Schafer remarks in the last edition of Quain 

1 Op. cit., p. 41c. 



APPENDIX 331 

(vol. i., part ii.), "All nerve-fibres and nerve-cells . . . are 
originally derived from the neural or neuro-sensory ectoderm." 
If these statements are true, one is led to the conclusion that 
odontoblasts cannot possibly be, from the developmental point 
of view, ganglion cells in which sensory or tactile or trophic 
impulses arise de novo. But it is no argument against the idea 
that they serve as sensation transmitters. 

Again, it is difficult to believe that odontoblasts serve merely 
as factors in the production of and keeping up the nutrition 
and vitality of dentine, for, as has been pointed out, they are 
practically absent from the radicular part of the pulp. If 
this were their office there would be no diversity of shape or 
size. Dentine is vitalised, in the opinion of the author, by a 
protoplasmic exudation which emanates from the blood-vessels 
of the pulp, and fills the tubules by surrounding and protecting 
and nourishing the fibrils. The pulp capillaries end near the 
odontoblasts, but do not enter the tubules. 

It is an extremely difficult matter to have optical proof that 
the telodendria of the nerves enter the basal extremities of 
the odontoblasts, as suggested by Aitchison Robertson. It 
would be different if the nerves did not lose their myelinic sheaths. 
The staining and demonstrating of these delicate threads 
would then be quite easy. But we have the presence of the basal 
layer of Weil, which exists in that part of the pulp which is most 
sentient. Pain from irritation and destruction of the fibrils 
begins in the crown and neck of a tooth, and not as a rule under ce- 
mentum; and Weil's layer consists of fine fibres which extend 
deeply into the pulp on the one hand, and into the basal ends 
of the odontoblasts on the other. The inference, therefore, 
theoretically and logically speaking, is that many of the fibres 
in Weil's layer are amyelinic nerve fibres. This can only be 
disproved by the difficult experiment of severing the main 
trunk of the nerve and cutting off communication with its 
centre, and examining the pulp for any degenerative changes 
that might occur. Gowers 1 wrote, "If a fibre is cut off from 
its parent cell it degenerates; the part still in connection with 
the cell does not degenerate." 

1 "Diagnosis of Diseases of Brain." 



33 2 APPENDIX 

As odontoblasts are largest and most important in the corono- 
cervical portion of the pulp; as their functions must be closely 
associated chiefly with this part — in consequence of their large 
size and importance; and as this part is that through which 
the nerve sensations chiefly reach the pulp via the tubules, 
therefore it would seem that the odontoblasts must be more 
intimately connected with the nervous system that has hitherto 
been supposed, and they must be the actual end organs or dental 
ganglia of the nerves of the pulp. And the corollary is that the 
term odontoblast is a misnomer. 



The Physiology of the Cells of the Pulp Proper 



Little remains to be said about the central cells of the pulp. 

The functions of the spindle-cells is probably a generative 
one — to produce new odontoblasts in places where the old 
cells have been modified by the advancing line of freshly 
deposited dentine. The round cells would seem to have a 
secretive property, in cases where secondary dentine or nodules, 
or calcareous degenerations are taking place, in addition to 
the all-important function of laying down the matrix of dentine 
in developing teeth. These cells, then, should be called odon- 
toblasts. 

These researches and arguments tend thus to shew what 
probably are the functions and uses of the cells of the pulp; 
it is at present impossible to say absolutely that this view is 
substantially correct. But until they are disproved, the reader 
may believe that the building of the dentinal wall of this organ 
does not depend on the integrity of the odontoblasts, but on 
the functions of the small secretory cells of the pulp proper; 
and that while the former are active agents, governing and 
protecting, as sense or trophic organs, its interior, their duties 
only ending at the death of the pulp, the latter are more passive 
agents, serving merely for mechanical purposes by secreting 
matrix or new dentinal formations during the life of the tooth. 



APPENDIX 333 

NOTE B 

PHYSIOLOGICAL (LACUNAR) ABSORPTION OF THE ALVEOLAR 
PROCESSES OF THE JAWS OF MAN 

The phenomena associated with physiological absorption — 
as distinct from pathological absorption of the hard tissues — 
are observed to a remarkable extent in the mouth. The 
teeth and their sockets exhibit these phenomena and reveal 
thus another trait in their unique character. 

It must be remembered that the bone of the alveolar proc- 
esses [of the jaws is a particularly transitory and unstable 
structure. Osseous tissue generally is frequently undergoing 
changes, and that composing the sockets of the teeth at an 
early period of life begins to show signs of degeneration. 

The teeth of man are degenerative organs and their alveolar 
attachments also. With regard to the latter, five reasons may 
be adduced: (i) Absence of muscular origins or insertions; (ii) 
atypical character of the structure of the bone; (iii) poor 
or inadequate blood supply; (iv) lack of function, and (v) de- 
creased physiological resistance to disease, as to retrogressive 
metamorphoses. 

(i) With the exception of a few fibres of the Buccinator 
muscle in the molar region there are no reflected or attached 
muscular tendons or fasciae in the neighbourhood of the teeth. 

(ii) As has been demonstrated in Chap. X., Vol. I, their 
histological elements differ very greatly from those of compact 
or cancellous bone. 

(iii) Near the terminal margins at the gum the m dullary 
spaces and contents of normal bone are generally absent, leading 
to malnutrition of the parts. 

(iv) The main function of the skeleton is to support the 
muscles of the body. This function is certainly lacking here; 
the main function of the alveolar processes is merely to afford 
attachment, by a fixed gomphosis, for the roots of the teeth. 

(v) As a consequence of lack of function, malnutrition and 
atypical character, resistance to disease is diminished and soon 
disappears. 



334 APPENDIX 

''Physiological absorption" "atrophy," "wasting" are syn- 
onymous terms. It occurs very early in man in the alveolar 
processes of the jaws. Not only does bone undergo this phy- 
siological absorption but, as was described in Chap. XI, dentine 
and cementum do also. This is exemplified on examining 
a vertical section of the jaws of a young mammal, e.g., a kitten, 
before the deciduous teeth are shed. Absorption areas of 
various sizes can be easily seen over the apical as well as the 
cervical portions of the deciduous teeth. The phenomenon 
is well observed also in the teeth of animals which have a 
polyphyodont dentition, such as the crocodile. 

The same process occurs through the operations of natural 
laws in the deciduous teeth of man. Persistent members of 
this set, even if not followed by any permanent successors, have 
their roots painlessly absorbed. In these cases the histo- 
logical process would appear to be identical with pathological 
ones. The hard parts are removed by the agency of osteo- 
clasts, and very frequently the process of repair may be seen 
going on side by side with the process of absorption. 

If dried skulls of children aged from four to six years be exam- 
ined, an instructive demonstration of the condition can be ob- 
tained as it applies to the shedding of the deciduous teeth and 
their sockets. There is here an obvious physiological absorption 
of the bone, the immediate effect being the thinning and destruc- 
tion of the tissues by a method similar to that which obtains 
in osteoporosis. Thus there is an entire absorption and com- 
plete loss of the sockets of the deciduous teeth occurring in a 
normal painless manner. With regard to this absorption 
Tomes 1 says: — "The alveolar portion of the jaw, that which 
lies above the level of the mandibular canal, is developed 
around the milk teeth; when they are lost, it disappears, to 
be re-formed again for the second set of teeth, and is finally 
wholly removed after the loss of the teeth in old age." 

The skulls of adults show a similar wasting of bone around 
the cervical and radicular portions of the teeth. Osseous 
atrophy over the labial surfaces of maxillary and mandibular 

1 A Manual of Dental Anatomy." Edited by Marett Tims and Hopewell- 
Smith, 1014. 



APPENDIX 335 

canines, over the palatal aspect of the palatine roots of max- 
illary molars, as well as in other localities is frequently observed. 

The changes undergone by the bone of the mandible are well 
known. Again to quote Mr. Tomes: 

"As the jaw undergoes increase in size, large additions are 
made to its surface by deposition of bone from the periosteum, 
necessarily lengthening the mandibular canal. The addi- 
tions to the canal do not, however, take place quite in the line 
of its original course, but in this added portion it is bent a little 
outwards and upwards. If we rasp off the bone of an adult 
jaw down to the level of this bend, a process which Nature in 
great part performs for us in an aged jaw, or if instead we make 
due allowance for the alteration, the mental foramen becomes an 
available fixed point for measurement. 

"The manner in which the jaw is formed might also be de- 
scribed as wasteful; a very large amount of bone is formed which 
is subsequently, at no distant date, again removed by absorption. 

"To bring it more clearly home to the student's mind, if all 
the bone formed were to remain, the coronoid process would 
extend from the condyle to the region of the first premolar, 
and all the teeth behind that would be buried in its base; 
there would be no "neck" beneath the condyle, but the in- 
ternal oblique line would be a thick bar corresponding in width 
with the condyle. It is necessary to fully realize that the 
articular surface with its cartilage has successfully occupied 
every spot along this line, and as it progresses backwards 
by the deposition of fresh bone, it has been followed up by the 
process of absorption removing all that was redundant. 

"On the outer surface of the jaw we can frequently discern 
a slight ridge, extending a short distance from the head of the 
bone, but if the prominence were preserved on the inner sur- 
face, the mandibular artery and nerve would be turned out of 
their course. We have thus a speedy removal of the newly 
formed bone, so that a concavity lies immediately on the inner 
side of the condyle; and microscopic examination of the bone 
at this point shows that the lacuna of Howship, those charac- 
teristic evidences of absorption, abundantly cover its surface, 
showing that here, at least, absorption is most actively going on. 



336 APPENDIX 

''In the same way the coronoid process, beneath the base of 
which the first, second, and third molars have successfully 
been formed, has moved backward by absorption cutting 
away its anterior, and by deposition adding to its posterior 
surfaces. 

"In old age, concomitantly with the diminution of muscular 
energy, the bone about the angle wastes, so that once more the 
ramus appears to meet the body at an obtuse angle. But all 
the changes which mark an aged jaw are the simple results of a 
superficial and not of an interstitial absorption, corresponding 
with a wasting of the muscles, of the pterygoid plates of the 
sphenoid bone, etc." [The author's italics.] 

To the above, two further instructive illustrations from 
comparative anatomy may be added. In Batrachia, e.g., the 
frog, the teeth are attached by their bases and external surfaces 
to a groove in the jaw, having the external wall higher than the 
inner, and also having on their outer side a new osseous forma- 
tion which slightly extends over the outer side of each tooth. 
The deficiency on its inner aspect is supplied by a long pillar, 
which disappears when the tooth is shed, a new column being 
developed for the succeeding tooth. 

And even a more interesting fact is observed in the mouth of 
the eel. Here the teeth are fixed to the jaws by means of a 
"bone of attachment." When the teeth are shed, the bone of 
attachment is shed also, being removed from the body of the 
jaw itself. This is effected by means of large multi-nucleated 
giant cells, which leave the surface of the bone scalloped out 
into Howship's foveolae. 

It is certain that the free alveolar edges of the jaws of man 
begin to disappear at a very early age. Radiographs show the 
commencement of the absorption of the bone around the roots 
of the deciduous teeth in the normal mouths of healthy children 
at the age even of four years. If radiographs of the jaws of 
healthy and normal adults aged twenty and more be examined 
the same thing is apparent. The free edges of the lamina 
dnrce disappear, while they themselves remain in their other 
portions intact. 

Examples need not be further multiplied; physiological ab- 



APPENDIX 337 

sorption is so obvious. Finally Hektoen and Riesman (A 
Text-book of Pathology, iqoi) write: — "it is generally believed 
that anaemia of bone favors absorption and hinders apposition, 
and it may be one of the factors in these forms of atrophy. The 
atrophy may be concentric or eccentric. It begins, as a rule, 
at those points that are free from muscular attachments. In 
the calvaria the bone becomes thin, granular and finely porous, 
especially in the temporal regions. An atrophy occurs in the 
external table; the internal may become rough from the pro- 
duction of new bone. In the maxillae the alveolar process may 
disappear completely." 

Bordering on the line between physiological and pathological 
absorption of bone, as witnessed in the alveolar processes, is that 
induced by the mechanical action of orthodontical appliances 
when a tooth is moved from one position to another. Ab- 
sorption occurs from pressure, on the side opposite to the oc- 
casioning force, while deposition of fresh osseous material takes 
place on the proximate side. 



INDEX TO VOL. I 



Abbot on enamel, 28, 33 
Abrachiate lacunae,- 201, 202 
Absorbent organ, 209 

Origin of, 200 

Osteoclasts of, 211 

Stroma of, 209 
Absorption, physiological, 333 
Addison and Appleton on 

Growth of teeth of rat, 299 
Aitchison Robertson on 

Growth of dentine, 291 

Xerve endings in pulp, 154 

Odontoblasts, 127 
Alveolar processes of jaws, bone of, 208 
Alveolo-dental periosteum, 166 

Black on. 16;, 168, 172, 173. 174 

Calco-spherite spherules of, 178 

Cells of, 169 

Epithelial "rests" of, 173 

Fibres of, 167 

Malassez on, 174 

Measurements of, 167 

Nerves of, 177 

Xoyes on, 173, 178 

Origin of, 166 

Osteoblasts of, 173 

Osteoclasts of, 173 

Principal fibres of, 167 

Sharpey's fibres of, 169 

Vascular supply of, 177 
Ameloblasts. 245, 250, 279, 281 

Cytoplasm of, 281 
Amyelinic nerve fibres, 135, 145 
Andrews, fibres of, 282 
Andrews on ameloblasts, 282 

On Xasmyth's membrane, 9 

On vascularity of enamel organ, 
261 
Antrum of Highmore, 223 

"Battledore" cells of, 225 

Epithelium of, 224 

Glands of, 226 



Antrum of Highmore, Goblet cells of, 

- 2 5 

Lining membrane of. 224 

Origin of epithelium of, 224 

Sappey on, 223 

Wall of. 205 
Arnell on ameloblasts, 2S2 
Axones, 142 

"Battledore," cells of antrum, 225 
Baume on origin of lip-furrow, 235 
Beaver, enamel of. 94 
Bennett on lamellae in dentine. 77 
Black on epithelial bodies in peri- 
odontal membrane, 174 
On gingival gland. 1 74 
Bland-Sutton on "Glands of Serres, " 

223 
On development of ovarian teeth, 

305 

Bodecker on enamel, 28, 32 

On Xasmyth's membrane, 10, n 
On nerve endings in pulp. 155 
On vascular supply of antrum, 224 

Boll on dentinal tubes, 69 
On nerve endings. 149 
On odontoblasts, 126 
On sheaths of Xeumann, 69 

Bone, structure of, 196 

Broomell on cementum, 86, S9 

Canine fossa, bone of. 198 
Capillaries of dental pulp, 137 
Cat, nerves in dental pulp of, 151, 152 
Cemental organ. 272, 302 
Cementum, Black on, 87 

Broomell on, 86, 89 

Development of, 302 

Distribution of, 79 

Incremental lines of, 85 

Magitot on, 302 

Matrix of, So 



339 



34Q 



Cementum, Measurements of, 79 

Modifications of, no 

Of opossum, no 

Origin of, 79 

Perforating canals of, 87 

Sharpey's fibres of, 87 

Walkhoff on, 84 
Cheeks, structure of, 181 
Choquet on relationships of hard tis- 
sues, 19 
Crescents of Gianuzzi, 189, 227 
Czermak, inter-globular spaces of, 69 

Demilunes of Heidenhain, 189 
Dental capsule, 212, 266 

Development of, 272 

Fibres of, 214 

Glands of, 215 

Origin of, 212 
Dental pulp, in 

Cells of, 115 

Measurements of, in 

Nerves of, 138 

Origin of, in 

Stroma of, 130 

Vessels of, 134 
Dentary centre, 195 
Dentine, 49 

Aitchison Robertson on growth of, 
291 

Bennett on, 77 

Contour lines of, 74 

Development of, 287 

Distribution of, 50 

Experiments in growth of, 291 

Granular layer of, 71 

Growth of, 291 

Homogeneous layer of, 73 

Interglobular spaces of, 69 

Lamella? of, 76 

Matrix of, 50 

Measurements of. 50 

Measurement of growth of, 291, 
295 

Modifications of, 100 

Mummery, on development of, 289 

Mummery, on matrix of, 50 

Odontogenic, fibres of, 52 

Of fishes, 104 



Dentine, Origin of, 50 

Osteo-dentine, 104 

Plici-dentine, 100 

Rose on varieties of, 49 

Schreger's lines in, 73 

Secondary dentine, 78 

Varieties of, 49, 100 

Vaso-dentine, 103 

Von Ebner on development of, 289 

Waldeyer on development of, 288 
Dentine of hake, 104 

Of Pristis, 102 
Dentinal tubes, 53 

Boll on, 69 

Branches of, 61 

Contents of, 63 

Courses of, 59 

Hohl on, 69 

Klein on contents of, 64 

Kolliker on, 57, 61, 62, 67 

Lent on, 69 

Magitot on contents of, 65 

Measurements of, 57 

Morgenstern on contents of, 65 

Neumann on, 65, 66 

Romer on, 67 

Sudduth on, 68 

Tomes on, 69 

Underwood on, 69 

Walls of, 63, 65 
Dentogenetic zone, 280 
Dependorf on innervation of dentine, 

154 
Development of dental capsule, 272 

Of dentine papilla, 245 

Of enamel organ, 238 

Of jaws, 19s, 303 

Lepkowski on vascular supply of, 
266 

Of osteo-dentine, 325 

Of plici-dentine, 325 

Vascular supply of, 262 

Of vaso-dentine, 325 
Development of teeth in cod fish, 314 

Crocodile, 319 

Dog fish, 316 

Human embryos, 303 

Lizard, 319 

Mammals, 231 



34i 



Development of teeth in Newt, 323 
Reptiles, 319 
Snake, 322 

Ebner on development of dentine, 
289 

On enamel, ^^ 

On enamel spindles, 43 

On matrix of dentine, 50 
Enamel, 17 

Amelo-dentinal junction of, 47 

Andresen on, ^t, 

Andrews on development of, 
282 

Appearances of, 21 

Arnell on development of, 282 

Of beaver, 94 

Bodecker on, 28, 43 

Bodies of, 31 

Choquet on relationships of, 19 

Development of, 280 

Distribution of, 17 

Encapsuled lacunae of, 13 

Of fishes, 96 

Of hare, 96 

Imbrication lines of, 26 

Kolliker on, 25 

Leon Williams on development of, 
285 

Of man, 21 

Of manatee, 95 

-Matrix of, 32 

Measurements of, 18 

Modifications of, 93 

Origin of, 17 

Of porcupine, 95 

Of rat, 94 

Relationships of, 19 

Of rodents, 94 

Of Sargus, 97 

Schreger's lines in, 37 

Spee on development of, 282 

Of squirrel, 95 

Structural modifications of, 93 

Sudduth on, 33, 284 

Thorsen on relationships of, 20 

Tomes on, 43, 281 

Tubular, 96, 281 
Enamel "bud," 238 



Enamel organ, ameloblasts of, 250 
Beale on vascularity of, 261 
External epithelium of, 244, 245, 

279 
Inner ameloblastic membrane of, 

251 
Internal epithelium of, 245, 279 
Leon Williams on, 245, 251, 252, 

279 
Membrana preformaliva of, 251 
Stellate reticulum of, 240, 244, 

245, 256, 261, 279 
Stratum intermedium of, 241, 245, 

252, 255, 261, 279 
Vascularity of, 261 
Enamel rods, 2r 

Abbott on, 28, 32, 33 
Bodecker on, 28, 32 
Curvatures of, 34 
Ebner on, 33 

Leon Williams on, 29, 31, 32, 37 
Of man, 21 
Measurements of, 25 
Pigmentation of, 29 
Striae of Retzius of, 35 
Sudduth on, t,t, 
Tomes on, 34 
W'alkhoff on, 32 
Enamel spindles, 39 
Bodecker on, 43 
Ebner on, 43 
Hertz on, 46, 47 
Hollander on, 43 
Paul on, 45 
Romer on, 41, 44 
Tomes on, 43 
Waldeyer on, 45 
Walkhoff on, 46 
Wedl on, 43 
Epithelial sheath of Hertwig, 174, 257, 
279 

Fibres of Andrews, 282 
"Formative ring," 293, 294, 296,297 
Fromman's lines in myelinic nerve 
fibres, 143 

Gaslerosleus, nerves in dental pulp of, 
144 



342 



Gianuzzi, crescents of, 189 
Gingival trough, 221 
Glands of antrum, 226 

Salivary, 187 

Of tongue, 186 
Gobius, nerves in dental pulp of, 144 
Goblet cells of antrum, 225 
Gum, Andrews on "Glands of Serres" 
of, 223 

Epithelium of, 217, 220 

Glands of, 222 

"Glands of Serres" of, 223, 261 

Papillae of, 221 

"Spiny" cells of, 220 

Tomes on "Glands of Serres" of, 
223 

Vascular system of, 264 

Hake, enamel of, 96 
Hard palate, bone of, 203 

Structure of, 191 
Haversian systems, 196 
Hektoen and Riesman on physiological 

absorption, 337 
Hertwig, epithelial sheath of, 174 
Hertz on enamel rods, 34 
On odontoblasts, 129 
Hohl on sheaths of Neumann, 69 
Hollander on enamel spindles, 43 
Homogeneous layer of dentine, 73 
Howes on vascularity of enamel organ, 

261 
Howship's foveoloe (lacunae), 209 
Huber on nerve endings in dental pulp, 

150 

IitBRiCATioN lines of enamel, 25, 26 
Incisures, 143 
Intercalary duct, 188 
Interdental septa, bone of, 202 
Intralobular duct, 187 

Jaws, bone of, 195 

Development of, 195, 303 

Klein on contents of dentinal tubes, 
64 
On odontoblasts, 328 



Kolliker on dentinal tubes, 61, 62, 63, 
67 
On enamel, 25, 36, 37 
On Nasmyth's membrane, 1 1 
On nerve endings in pulp, 154 
On odontoblasts, 121 

Labio-dental strand, 235 

Lacerta agilis, nerves of pulp of, 145 

Lacuna;, abrachiate, 201 
Of bone, 197 

Lamellas of bone, 197 
Of dentine, 76 

Lamina dura, 169, 203 

Layer of Weil, 130 

Leche on origin of lip-furrow, 235 

Lent on dentinal tubes, 69 

Leon Williams on development of 
enamel, 285 
On enamel, 31, 32, 37 
On secreting papillas, 245 
On stratum intermedium, 245 
On vascularity of enamel organ, 
285 

Lepkowski on vascular supply of den- 
tal tissues, 266 

Lingual tonsil, 186 

Lips, structure of 181 

Lip-furrow, 234 

Baume on origin of, 235 
Leche on origin of, 235 
Rose on origin of, 235 
Sudduth on origin of, 235 

Lizard, development of teeth of, 319 

Low on mandible, 195 

Lymph nodes of tongue, 186 

Magitot on contents of dentinal 
tubes, 65 
On nerve endings, 152 
On odontoblasts, 127 
On sheaths of Neumann, 68 
On vascularity of enamel organ, 
261 
Malassez on "rests" in periodontal 

membrane, 174 
Manatee, enamel of, 95 
Mandible, bone of, 205 
Low on, 195 



343 



Marett Tims on vascularity of enamel 

organ, 261 
Maxillary sinus (see Antrum). 
Meckel's cartilage, 1951 2 3 2 
Mice, nerves in dental pulp of, 148 
Morgenstern on contents of dentinal 
tubes, 65 
On nerve endings, 156 
Mucous glands, 189 

Crescents of Gianuzzi of, 189, 
227 
Mucous membrane of antrum, 223 

Of mouth, 217 
Mummery on development of dentine, 
289 
On matrix of dentine, 50 
On nerve endings in Mammalia, 
158 
Myelinic nerves of pulp, 140 
Axones of, 142 
Crosses of Ranvier of, 143 
Fromman's lines of, 143 
Incisures of, 143 
Internodular segments of, 143 
Kolliker on, 154 
Method of distribution of, 140 
Myelin sheath of, 143 
Neurilemma of, 143 
Nodes of Ranvier of, 143 
Schafer on, 158 
Structure of, 142 
Terminations of, 144 
In fishes, 144 
In mammals, 148 
In reptiles, 145 

Nasmyth's membrane, 9 
Andrews on, 9 
Bodecker on, 10 
Cellular layer of, n 
Development of, 279 
Distribution of, 9 
Kolliker on, n 
Lacunae in, 13 
Measurements of, 10 
Origin of, 9 
Of ovarian teeth, 16 
Paul on, 13 
Translucent pellicle of, 13 



Nervous system of periodontal mem- 
brane, 177 

Of pulp, 138 
Neumann, sheaths of, 65 

On contents of dentinal tubes, 66 
Neurilemma, 143 

Newt, development of teeth of, 324 
Noyes on alveolo-dental periosteum, 
178 

On osteoblasts, 173 

Odontoblasts, 116 

Aitchison Robertson on, 127 

Analogies of, 129 

Boll on, 126 

Hertz on, 129 

Kolliker on, 121 

Magitot on, 127 

Paul on, 119, 121, 122, 129 

Processes of, 126 

Relationships of, 121 

Rose on, 115 

Shape of, 116 

Size of, 121 

Structure of, 122 

Transitional tissue of, 122 

Underwood on, 119, 330 

Waldeyer on, 121 
Odontogenic fibres, 52 
Opossum, cementum of, no 
Ortho-dentine, 49 
Osteoblasts, 173 
Osteoclasts, 173 
Osteo-dentine, 104 

Development of, 325 
Osteoid dentine, 109 
Owen's lines in dentine, 74 
Ox, nerves in pulp of, 154 

Odontoblasts of, 127 

Palate, 191 

Bone of, 203 

Papilla palatina, 192 

Soft palate, 191, 192 
Papillae of tongue, 182 

Circumvallate papillae, 184 

ConicaL papilla?, 183 

Fungiform papilla?, 184 

Gustatory cells of, 186 



344 



Papillae of tongue, Schafer on, 184 
Parotid gland, 187 
Partsch on basal layer of Weil, 132 
Paul on enamel spindles, 45 

On Nasmyth's membrane, 13 
On odontoblasts, 119, 121, 122, 

129 
On tubular enamel, 98 
On vascularity of enamel organ, 
261 
Paulton on vascularity of enamel 

organ, 261 
Periodontal membrane (see Alveolo- 

dental Periosteum). 
Periosteum of bone, 197 
Physiological absorption, Hektoen and 

Riesman on, 337 
Plici-dentine, 100 

Development of, 325 
Pont on nerves of the pulp, 160 

On odontoblasts, 161 
Porcupine, enamel of, 95 
Primary epithelial inflection, 234, 278 
Primitive dental furrow, 233 
Pristis, dentine of, 102 
Pulp, arteries of, 134, 136 

Basal layer of Weil of, 130 

Capillaries of, 137 

Cells of, us 

von Ebner on basal layer of Weil 

of, 133 
Mummery on basal layer of Weil 

of, 132, 134 
Nervous system of, 138 
Partsch on basal layer of Weil of, 

132 
Supporting fibres of, 122 
Veins of, 137 
Weil on basal layer of, 130 

Rabbits, nerves in dental pulp of, 149 
Ranvier, crosses of, 143 

Nodes of, 143 
Raschkovv, plexus of, 140, 164 
Rat, enamel of, 94 

Growth' of teeth of, 299 
Retzius on nerve endings in dental 
pulp, 144, 145, 148 

Striae of enamel of, 35 



Romer on enamel spindles, 41, 44 
On nerve endings in pulp, 153 
On walls of dentinal tubes, 67 

Rose on odontoblasts, 115 

On origin of lip-furrow, 235 
On varieties of dentine, 49, 108 

Russell's fuchsine bodies, 221 

Salamander maculata, nerves in pulp of, 

148 
" Salivary corpuscles," 194 
Salivary glands, 187 

Acini, 188 

Ducts of, 187 

Structure of, 187 
Salter on secondary dentine, 78 

On cementum, 86 
Sappey on antral glands, 223 
Sargus ovis, enamel of, 97 
Schafer on myelinic nerves, 158 

On nerve endings, 158 

On origin of nerves, 330 

On papillas of tongue, 184 
Schreger's lines in dentine, 73 

In enamel, 37 
Schultze on axones, 142 
Schweitzer on supposed pulp lym- 
phatics, 137 
Secondary dentine, 78 
Serous glands, 190 
Serres, "glands" of, 223, 261 
Sharpey's fibres, 87, 169, 197, 198 
Sheaths of Neumann, 65 

Boll on, 69 

Hohl on, 69 

Lent on, 69 

Magitot on, 69 

Romer on, 67 

Sudduth on, 68 

Tomes on, 69 

Underwood on, 69 
Snake, development of teeth of, 

322 
Spee on ameloblasts, 282 
Spiny cells of gum, 220 

Of Nasmyth's membrane, 13 
Squirrel, enamel of, 95 
Stratum intermedium, 241, 245, 252, 
255, 261, 279 



345 



Stellate reticulum, 240, 244, 245, 256, 

261, 270 
Stohr on alveolo-dental periosteum, 
166 

On cementum, 87 
Sublingual gland, 187 
Submaxillary gland, 187 
Sudduth on enamel, 33 

On sheaths of Neumann, 68 
Sympathetic nerves of pulp, 144 

Tomes on dentine, 49, 70 

On dentinal tubes, 69 

On enamel, 34, 281 

On enamel organ, 261 

On enamel "spindles," 43 

On "glands of Serres," 223 

On odontoblasts, 327 

On osteo-dentine, 108 

On physiological absorption, 334, 
335 

On sheaths of Neumann, 69 
Tongue, glands of, 186 

Lymph nodes of, 186 

Muscles of, 181 

Papillas of, 182 

Taste buds of, 186 
Tonsils, lymphoid cells of, 193, 194 

Lymphoid follicles of, 193 
Tooth-band, 234, 278 
Trabecular dentine, 108 



Translucent pellicle of Nasmyth's 

membrane, 13 
Triton cristatus, nerves of pulp of, 148 
Tubular enamel, 96 

Underwood on cementum, 90 
On odontoblasts, 119 
On sheaths of Neumann, 69 

Uvula, structure of, 192 

Vascularity of enamel organ, 261 
Vaso-dentine, 103 

Development of, 325 
Vitro-dentine, 49, 108 
Vitro-trabecular dentine, 109 
Veins of the pulp, 137 

Waldeyer on development of dentine, 
288 

On enamel spindles, 45 

On odontoblasts, 121 
Walkhoff on cementum, 84 

On Dental Histology, 4 

On enamel, 32 

On enamel spindles, 47 

On odontoblasts, 327 
Wedl on vascularity of enamel organ, 

261 
Weil, basal layer of, 130 
Welcker on dentinal tubes, 60